ill be honest with you man there are loads to reasons why this is happening. TLDR at bottom (please at least read it)
one of them is a extreme lack of communication. rioters rarely say anything at all anymore aside from the big red posts that happen every once in a while.
another is lack of action. some things stay stupidly strong and to the opposite of the scale nearly unplayable for very long periods of time.
not to mention the whole dynamic que thing, where they forced us into it when we said we dint want it, then when we said we dint like it and wanted a revert to solo/duo and ranked 5's back they told us we would get it. then did nothing, and told us it was still coming. the entire year. it did not happen till next season.
another is lack of listening to feedback aside from skins. i understand the gameplay teams(s) are separate from the art team(s).
unless some things are clearly out of line (which happens a lot and im not sure why) the community at large gives it a good chance. but once this this is over and its stated that the change is problematic or worse then what we had before they just dont really do anything.
a REALLY big one is damage and mobility creep. when it comes down to it the game has gotten more and more damage added into it through various means. the thing isnt instead of nerfing things that are too strong, they're buffing things up to their levels. over and over again.
(other than supports which seem to have the opposite problem. of everything being nerfed around them then being nerfed for still being able to do their job)
we're almost at the end now. change for the sake of change.
i can can understand why this happens but the result never works out.
now im not saying riot can achieve perfect balance for their game (which frankly is a pipe dream and in their best interests not to) but they should aim for at least a somewhat good balance.
champs often get changed just because theyre not the most played. their kit might not even be problematic or oppressive or their visuals outdated but they get reworked or receive some weird change that causes of problems for players(losing their main, losing a playstyle etc) or outright make them too strong which leads into my next bit.
buffs and nerfs that are out of line happen way more often than they should. champs that are otherwise fine (or strong but not top pick) in the meta will get buffed alot to make them be able to compete with with the top picks. rather than just nerfing the top picks.
and finally. they never admit they messed up. we can point out all the problems with something, how bad it was to implement for everyone involved, how it shouldnt have been shipped to live how it was etc etc. but they dont seem to actually take any of it in.
its frustrating.
TLDR: riot fails to communicate much at all, reacts at a mind numbingly slow pace to balance, often ignores feedback aside from skins, change for the sake of change, lack of ability to admit fault.
all of these lead to being frustrated, and we've only been getting more and more frustrated over the years.
eventually you see that calm discussion isnt working, so you begin to switch to outrage at the hopes of getting something across.