I've been playing lol from season 1, last year i got bored of playing, and it was hard to realize what pushed to the decision to stop playing this much. I just couldn't realize it, the game i loved, has started to bore and even annoy me. It was not like i had no time, or something in my mindset just changed and i didn't like the game in general.
So, i started playing DotA 2 (was playing original DotA maybe 10-8 years ago), it was kinda hard to adapt, totally different controls, different strategies and so on. I've got in love with it. Was playing for about a year. Played ~1 LoL game in a month, what i started to realize, that the thing, that pushed me out of LoL is community, this giving up in all games, constant flame. Flame is not a bit deal, because you can mute players, the big thing, is leaving game/afk. It's 10x more common in LoL.
My suggestions, is to punish way more harsher players, for leaving/afk in a game (like in DotA, low priority games, that you have to win, after being afk or leaving a game). OR. Make normal games more rewarding, because i feel like less and less players are playing ranked games like normal games: trying different champs that they have no clue about it, or just playing while bored/ tired, while they should play normal games instead.
TL;DR: LoL should punish afk/leavers more harshly, or make normal games more rewarding, so players would play more normal games for fun, instead of ranked.