People can't take criticism. They don't want to hear that they might not be doing something correctly or how to improve. They assume they know best. They don't look beyond their own lane/jg and see what everyone else is ACTUALLY having to deal with in their lanes/jg.
Lane x for instance goes 1/3/0 but is up 30 cs and has been repeat ganked every time they leave tower and been roamed on with no mia by a fed laner from another lane. They can still win 1v1 despite being so heavily focused.
Lane y fed their lane opponent 1v1. Due to jungle help though, they are 3/5/1. They are playing super passively at all the wrong times, never warding, and hiding under tower refusing to push even when their lane opponent is sitting in lane x for a full min waiting for said player to push out.
Lane y calls lane x toxic trash because lane x told lane y to get off their butt and push out when their lane opponent is sitting in lane x for a full minute while lane y is doing nothing.
So the lane x that has had to deal with either 1v2 or 1v3 all game (assuming solo lane) or else 2v3 or 2v4 all game (assuming lane x is bot lane) is considered trash because they have a lower kda. Despite the fact that they are actually more skilled than their opponent, that they've actually set up their teammates for great counter-gank opportunities which could have given them a positive kda, and despite the fact that they are STILL even after having been camped for 15+ minutes by people they didn't feed.
Meanwhile lane y - which has been given a 2v1 or a 3v2 for 15+ min cannot win their lane, refuse to push and consequently don't punish their lane opponent(s) for roaming to other lanes, cost their team towers (in their lane and other lanes), prevent their teammates from punishing their lane opponents, and cost map objectives (baron, drag, jungle camps). Somehow because they are 3/5/1 though, most people see this as much better than the 1/3/0 laner. And that someone with 0.33 kda would lecture someone with 0.8 kda about what they should be doing is inconceivable and toxic - no matter how nicely it is done or how valid their point.
People are lazy, arrogant, blind, and selfish. This has only gotten worse over the years - and I'm not saying this because I'm older. To give an example outside of league...
When I was younger, little kids sat in the front of the bus. We didn't talk to the older kids or look at them funny unless we wanted to get the crap beat out of us. When I was middle aged kid, stuff still held true. When I got to be that older kid sitting in the back of the bus, the little kid could turn around and cuss the crap out of anyone and if an older kid put him in his place, the older kid got punished and was a horrible person for doing that to some "innocent" little kid. Hell a friend of mine got sick of this one kid and convinced him to powderize some smarties and sniff them. It really stung his nose, but he did it a second time. Next day, my friend gets detention for it while the kid got nothing for having cursed repeatedly and talked shit to everyone. Instead of society teaching the little punk a lesson, it punishes the people who try to teach people to have some damn respect for others and that people who don't show respect need to be taught it - sometimes painfully. Don't know why society keeps heading further in this direction, but my guess is when all these kids become adults and experience THEIR CHILDREN acting towards them the way they acted towards others (and had society pretend such blind selfish rudeness was ok) they will be like "hell no". Then it will swing the other direction.