Why has Riot done NOTHING about this?

It is both the riot's and the player's, but mostly the player's. I disagree about how the players should be blameless. They have a clear choice to make: should I actually learn a new role, or should I troll. If they choose to troll, the blame falls upon them.

This game I just played was in high plat, the troll had enough champions and runepages, but just felt entitled to jungle. If you decide to troll just because you did not get your main role, you should be punished plain and simple. This may be different for lower level people who just do not have the resources or the chance to learn new roles, but it is inexcusable later on.

I mean, seeing as how buying champs iwth IP seems to be stigmatized in my experience, it takes a lot of time to work to buy new champs, and runes cost rp, that's a good few years before someone's allowed to play ranked.

Not fun for anyone.

Yeaaaaaah.... no. If people were to shift all the blame onto Riot, then what would stop half of the player base from simply not owning support champions and saying "Sorry, don't have any supports or rune pages. Can't play support." That's just a bit too close to being a cop-out answer for any player who gets autofilled to a role they don't want to play. Sooner or later, everyone is going to be autofilled into a role that they don't necessarily want. It's just a part of playing ranked, and it's not the end of the world. All they have to do is suck it up, play the match to the best of their ability - play safe if you aren't comfortable in the role, and let yourself be carried by a teammate who IS comfortable in their role, and then move on to the next match. Sheesh! I'm a support main, and even I get autofilled to roles other than support.

As far as Riot not giving players the necessities to play all roles... playing ranked is not a necessity of the game. It's a privilege. Riot already restricts it by making sure that players are at least level 30, and that they own a certain number of champions, to try and make sure that they have the basic game knowledge before turning them loose on their MMR. It's the player's own lack of foresight if they are not prepared with a suitable champion or rune page for each potential role they could encounter.

Back to the OP - I suspect one of the main reasons it hasn't been put in place is because of how many different ways it could be abused. The topic has come up many, many times here on the boards, and players are justifiably frustrated by the seeming lack of punishment for trolls. Since the IFS was instituted, Riot has steadily been working on ways to tailor that system to better detect trolling and intentional feeding. It is a bit more difficult than some of the other types of ToS violations though. Is Player X intentionally feeding or just having a bad game? That question can sometimes be difficult to answer, so much thought has been going into how the system would review those reports, in effort to prevent innocent players from being punished by mistake.

In cases like yours, with a champion select troll, who is simply wasting everyone's time because they do not like their role, people seem to be on the fence about whether reporting someone in champ select would be a good thing or not. Especially in flex-queue, when/if groups of 4 are allowed (not sure if they are back up and running now or not, since I don't play flex), it could just as easily be abused to try and force the fifth player to role-swap. And if the player refuses to swap, boot them. Then they get a 5 minute delay, and the group gets to move on to the next victim.

I dislike dealing with the champ select trolls just as much as you do, but I am not sure that this is the best way to solve the problem. We may need to trust in Riot to keep brainstorming on this one until something can be found that won't have quite such an easy way to be manipulated.