The problem with ARAM is people play terribly and if you're actually trying to play well, it's pretty frustrating. People mess around and then are like "it's just ARAM bro" when you're like "yo wtf plz actually play properly".
In general, League is a frustrating experience because it's basically inevitable that even when you're playing your absolute best, others on the team aren't. The occasional great experiences where everyone has that synergistic gameplay and excellent coordination/execution makes it all worth it (I guess), but every other match has me wondering "why am I still playing this?" heh