TT is actually quite popular of a gamemode. Majority of players do not play TT, but then again those same players also don't play 5v5 flex. TT is here to stay, there was just an issue with players having a looping bugsplat (I think it was for kayn players but it could be a wider issue). Yesterday I had a game where our jungler was a Kayn and he couldn't connect to the game and just kept reconnecting all game only to get disconnected again. Me and Garen pulled through and still won since we were against a yuumi. Removing TT or moving it to be a RGM would quite possibly be the worst mistake Riot Games could make as it wouldn't push those players to play 5v5 more but instead cause anger and rage reducing the player count or creating toxic players.
EDIT: everyone plays ranked TT. I do not recommend playing blind pick TT since from my experience it results in a high percentage of bots ruining games. Ranked TT has a high player base but nobody plays blind pick for this reason. I can't wait for ranked TT to be back up.