This problem is mostly down to the way that top lane's meta works.
Top Lane, if you look into it, has the highest number of champions who are "viable" in the lane (as in, even champions that aren't strong right now like Quinn or Maokai top etc).
Not only that, but then look at the classes of champions that go into the lane: Divers, Fighters (Dunno the proper term here, i assume just "fighter, but basically i mean stuff like Jayce/Wukong, basically the slightly tankier assassin type stuff who build full damage), Tanks, Marksmen, Juggernauts, Various types of mages, and thats before we even get into the oddball champions like Teemo/Gangplank/Kayle.
This mostly came about due to the way that league used to design champions less around a specific kit/role in mind, and more just with "lets see where it goes" type of mentality. You can see this if you look way back into things like the old versions of Maokai and gangplank for example, they weren't specifically designed for top lane in mind, just sorta designed a cool champion. Over time Riot's design philosophy would change. But this kinda left a lot of champions in a weird limbo state where "what the hell do i do with them" was a common response to where you were supposed to play them. Look at stuff like Jayce, the old Gangplank or even to something like Heimerdinger. In a player's mind, theyre clearly solo laners because theyre not adcs, they arent really great junglers, which leaves mid and top. Mid at the time was overrun with mages, before Zed's release heralded the return of assassins into the meta, so a lot of the time, these champions went unnoticed until someone figured out "Oh hey, every bruiser gets shit on by these guys. Why not take them top?"
Traditionally, way back in season 1/2 or so, top lane was usually the 1v1 lane, primarily due to the lack of a rift herald and top side objectives at the time. Bruisers naturally excelled in this environment, and at the time, had much stronger early games relative to their lategames. Champions like the old Irelia and Shyvana were pretty good during this time, and as other lanes slowly got power crept, traditionally mid-centric champions like Kennen would phase into top lane as a lane bully, as range differencial was very rarely accounted for (and still isn't to this day).
This is basically a really fancy way of saying that top lane is a clusterfuck. Theres champions that fulfill completely different roles in teams and have completely seperate win conditions and power curves, then when other lanes get powercrept with new releases, often times champions are relegated into top lane. (Some examples of champions designed for other lanes that became top laners due to power creep in their traditional roles: Old Akali, Old Kayle, Old Fiora (iirc she was designed for mid, someone correct me if im wrong), Old Urgot, Old Maokai, Heimerdinger, Viktor (specifically his tank build in s7/8), Lissandra (not currently, but in the past).
Top lane of course isn't unique in this regard. This also happens a tonne with supports, especially with the addition of Season 4 and onward's gold generation items, some examples off the top of my head are Nautilus, Old Zyra, Post-Rework Malzahar (but before his voidlings got adjusted), Vel'koz, Xerath, Brand and perhaps my favorite example, Leona, tho she failed in her intended lane right away before getting relegated.
Top lane is basically a conglomerate of balance nightmares. Every change that occurs to items, champions and runes, will likely affect top lane in addition to the lane its intended to affect. For a recent example, the fleet footwork buffs some time ago made Akali's top lane much stronger, while the buff was intended for ADCs.
There's a great quote from a league player, who's name escapes me, but he's a famous top lane streamer. It was something along the lines of "Top lane is the only lane where a player can pick a champion to make you useless. Sure playing against Malzahar as (old) Katarina is hard, but you at least have a window of opportunity to do something for your team, in top lane, if you pick Jax or Darius and the opponent picks Kennen, its already over unless they don't understand gameplay fundamentals".
Just my general thoughts on the matter. Its not really Riot's fault in particular, though they do tend to listen to a CERTAIN class of champions more than others when it comes to balance matters, they generally do a good job for everyone. The exception to this, in my personal opinion, is Top Lane's ranged champion problem. I still don't understand why the only lane where a champion like Darius is viable, why champions like Kennen, Ryze and Jayce are also allowed to be viable in the same lane, while riot continually looks for ways to remove hard counters from other lanes and make them into soft counters (such as w/ the QSS nerf vs Zed R or the changes to tenacity stacking), it almost feels like everyone else isn't allowed to have true hard counters but top lane.
I think a lot of the issue comes down to riot often forgetting about top lane's conglomerate nature, and attempting to conform every one of the vast categories in top lane into one specific build or role.
Conqueror is a pretty great example of this, for Bruisers. I think people are too quick to forget that Bruisers didn't have an actual keystone until conqueror dont even try to @ me about Press the Attack either, thats far from a viable option on 90% of the current conqueror users came. It was so bad that champions like Tryndamere and Xin Zhao were using Electrocute. Conquerour was basically a "catch all" rune for Bruisers, since it needed to fulfill the widest group of champions, thus the rune is basically fucked from the get go. Its a grab bag of effects, from damage stacking to tank killing to sustain, it does so many things because the category of "bruiser" is so vast that the champions in that category want different things. A champion like Jax might want the stacking damage, where as a champion like Aatrox might want the sustain, while also needing the tank killing in most cases.
This basically forces the rune into a state where its a jack of all trades, novice of all, and making it's strongest abusers seem like the "average" performance of the rune (see Riven), while other champions using it like Aatrox or Darius aren't nearly as abusive with it overall, and thus forcing Riot to take measures in making items and other options for Bruisers less powerful. Its too late now to change conqueror's mechanics just on its own, since you'd create another major meta shift. Honestly it'd require a Class Update tier rework to the entirity of the Bruiser/Diver class/items/runes. The dream would be that runes would be split up, one sustain rune, one damage stacking rune and one tank killing rune (kinda like how ADCs get to have Fleet, Lethal and Press among others...), but so many balance changes have already been made because of Conqueror's impact on the lane that its too late to do anything minor. I suspect we'll see more slow nerfs to Conqueror and buffs to Tanks until top lane becomes League of Tanks again. Hell even at MSI you can see the lack of Conqueror present already, and thats before 9.10.
Honestly theres no solution to Top Lane, if Riot wants to keep top lane as the "wild card" lane it is today, with everything ranging from Ryze to Jax to Kayle, then nothing is going to fix it. The only hope is that Riot focuses in on the classes they want top lane to be for (based on player population, that'd likely be Tanks and Bruisers), then balance around that, and move champions who aren't in that category into other lanes, but doing that would be such a massive hassle that it's never going to happen. Its sad, since theres a tonne of champions that will never function in other lanes seriously, just due to how theyre structured.
The RIP list, for champions forever stuck in top lane (for high elo/competitive at least):
Apologies for this being so rambly and long. Not too good with the whole "eloquence" thing.
can just go top and make melee champs useless is proof that Riot doesn't know what to do with top lane
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