As people have already seen (probably to a little bit of rage), TFT is still blowing up and still immensely popular. Of course this continues to beg the questions that are _constantly_ asked by Boards:
"Who even LIKES TFT!?"
"IDK man I don't know anyone who plays this."
"Honestly after one game I got bored and quit BUT I did play Nexus Blitz for hours."
Simply put? Not you.
The thing about TFT that people continue to ignore or just not even think of is that TFT was essentially Riot's attempt at an entirely new game in the league client...which also fits their desire for it to essentially be Battle.net/Steam/EGS/etc. where you can play all of Riot's games from this one launcher. TFT also does something no other game mode did: Capture a different audience. People who would never even touch league or are wholly uninterested in it want to play it. People who don't like MOBAs play it and as such, it brought in a fresh, new audience.
"But they killed other modes I liked because of it!"
That sucks but honestly, the proof is there. There are people who play PvE games like Left 4 Dead, Overwatch's Seasonal events, etc. Yet despite it, the graph shows that people just weren't invested in it. Now, granted, Riot could do more to show off these things. Even still, the drop rate of these PvE playerbases show that the community just wasn't there.
And more importantly, we forget that as a video game publisher, Riot doesn't just make one thing. Even companies known for one series (FromSoft + Dark Souls) make other things as well. Blizzard was an RTS juggernaut but has expanded into card games, FPS, MMOs and more. Each one attracts a different audience.
Instead of hating TFT and hoping it dies, maybe instead think of what genre you would be invested in? I love city builders, as an example, and I'd explode with glee if I knew Riot was going to make some weird Runeterra city builder where I get to make my own little town, maybe make some champions in it, etc. It's also something I know would get fragged the fuck out if someone saw that Riot was putting resources towards anything other than League.
#TL;DR TFT is popular because it appeals to a completely new audience. It's a new game, not a game mode like Riot is trying to push. Instead of hating on TFT, maybe consider what Riot should go into next.