The balance team is accountable to the company (they are Riot employees), and are forced from above to introduce changes that put certain champions in the limelight, or are ordered to not touch incredibly frustrating, problematic, long-standing broken, and recently released ludicrously overpowered champions because that would affect Riot's bottom line.
If a single person with some decision making leverage employed at their balance team had a backbone and acted on it, they would lose their job very quickly. Balance changes for the better go against profit motives, at least with the way the game is set up. Champions that aren't played sell no skins - why would they dare touch the mid lane cash cows a la Zed, Yasuo, Qiyana and more. I can't think of a recent champion release (ignoring long-standing garbage like Zed) where I had the thought Yep, I had a reasonable experience playing against this character
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This isn't even some insane redpill conspiracy theo...