In general, finding PvP games on lower level accounts is fairly difficult. I don't have data on the player population and such so I can't claim anything to I say to be true, but I imagine most players speed level their way to 30 using exp boosts playing against bots. There's so much that is unpleasant about playing normal games on a new account.
You don't own many champions and the only way to obtain BE in any appreciable amount is by leveling. But exp rates are abysmal (although better than before they reworked it), you don't get full access to rune pages early, and PvP games are hardly enjoyable because of smurfs, toxic players (there's a reason these people had to make a new account, eh?), etc. And, mind you, you're waiting for quite some time to run into all of this.
All of these reasons are convincing me that the only way to play on a low account is get an exp boost and go play bots. Another thing to mention is that, previously, you earned IP for playing games. That is no longer the case. Now, most of the BE earned is locked behind your summoner level. If you sped through to level 30 before, you would be at an IP shortage because you played fewer games. Now, since BE isn't time-gated (outside of FWOTD, although that's hardly relevant), most players I assume would rather just exp boost bots to 30.
If you're a new player learning the game, PvP games are probably not very enticing. If you're a veteran player, you probably don't find the PvP games worth your time. To reduce queue times, you can get into a premade with other players (I recommend level 30+ so you get matched with the majority of the player base.... queuing with another smurf hasn't helped much in my experience).
I suppose another possibility is that matchmaking is just wonky.