A team deathmatch where we can pick the champion we want

Why don't we have one? We have a permanent team deathmatch mode called aram but you're given a random champion. These extra/random modes like Legend of the Poro King, Random URF, Star Guardian (whatever that was called) etc are complete trash, why does it make too much sense for Riot to let us pick the champion we want in a team deathmatch mode? Also anyone who says "well people will just pick the OP" you're only saying that because you suck and have no confidence, stick to aram.

It seems like Riot's logic is "lets give them random modes, and make most of them a mode where they are given a random champion". Random, random, random. League of Legends is my favorite game to team fight in and it frustrates me that all we have is aram where you will be given a random champion that you don't want to play, or a mode every 1-2 months that lets you actually pick the champion you want. It makes no sense and it seems like Riot isn't going to go away from this "give them a random mode every few weeks" direction.