I played TT and I'm among those, who think that mode was horrid. The game was designed for 5v5, a lot champions followed that principle. Due to this principle, it could never be balanced, because in 3v3 champions who are otherwise not really overloaded in the classic 5v5 can quickly become super oppressive in TT. Prime example is Kayn. Kayn isn't that oppressive in Summoner's Rift, because the map is bigger, but in TT he was a must pick in Jungle. Not to mention Supports were close to irrelevant there, because simply you played 1 Top 1 Jungle or 1 Bot, otherwise you are at disadvantage if the enemy runs this setup.
TFT isn't the reason nobody liked TT, that's just finding a scapegoat. TT was never really good and was never really popular, no matter how hard Riot tried to balance it, it's just unbalanceable and because people didn't really play it nor did they were bothered by its existence, so Riot left it in, but LoL just got expanded when TFT was introduced and I can imagine the game could get even bigger, so they retire a gamemode which was from days long gone by to save resources.