Most the time when Y calls for the team to report X, X reacts in a negative manner and then goes into a "tilt"y state.
You can call it that a lot of people are very sensitive, as if they have a thicker skin, then they can just shrug it off. But most people don't take that negative comment against them very well. It's kidda like league's way of calling someone noob.
Of course, I see people tell the enemy team to report their team mates, and most the time I ask them what it is for. They either say "feeding" or "unskilled".
"unskilled" no longer exists, not that it did anything back in the days other than adjusting some match making elements.
Alot of people misunderstand "feeding" and "intentional feeding", which are very very different and most people don't seem to understand that.
If X were to say in /allchat to report a Y for toxic, and I can't read their chat, chances are I'm not reporting unless I see toxic stuff in /allchat. But that does give me slight grounds to monitor X, as if it is a common thing they are doing, they are on grounds of "starting" the negativity instead.
You can see all these threads complaining about them just trying to defend themselves. Which means there are always a bunch of others calling to first "report a team mate" or "calling them bad/noob". The cycle continues and both parties get banned.
Making sense?