Why are some champs left in a garbage fire state?

This is more a philosophical question for the balance team - admittedly, I'm tilted from trying to play a game as Morde just now, but this has been a continual problem. A handful of champs are left to rot for months or years (see: eve, olaf, singed in years past; currently, Ryze - short duration, Morde, Aatrox (non-devourer), Illaoi, probably more), while others are continually iterated on.

Having a niche is one thing, but deliberately handicapping players who would like to play a subset of champs just sucks, frankly. When you're flat out told after the game "should have picked an A- or S-tier champ", that's a problem. I understand balance is hard, and there's a huge roster, so a decent job is probably being done...but how hard is it, really, to look at the last ~3-5 rolling patches and target champs that are underperforming across the spectrum? Hell, you've done it for Renek/J4/hecarim in this patch (not that the proposed changes are going to help them 2+% win rate like they need, but still...

Why is letting champions rot okay?