Why are french gamers so toxic?

Agree, there are lots of toxic players in overwatch.
From all countries.
Calling names are usually the easiest(most fun for some) words to learn in another language.
Doesn’t matter how they are toxic; if they just call names, leave games, be racist, one tricking etc… , it is what you can get when you play with the random group creator.
There will never be a AI system that will match you with the ideal group members in overwatch. Not even when they introduced other systems like role queue.
The only way to make sure you like the people you play with is to find those people yourself.

Don’t complain about something just because you are too lazy to do it yourself.
LFG is still not perfect, but from time to time you find people to add to your friendlist. So you can create 6 stacks without help.