My entire experience with MOBAs is that people will rip you to shreds for not doing or knowing every overly specific thing people didn't know either when they had less experience.
Not really about being anonymous as I've seen the same pattern when playing with people I know in real life, although playing with strangers removes a lot of restraint.
It's more that those games create a scenario where you are going to be frustrated for 20+ minutes because of mistakes of others, and you likely started playing because you're trying to get away from frustration IRL.
Unfortunately I can agree with this completely. I stopped playing Fortnite because of this. Although it can be fun without winning, when they introduced the victory crowns to reward multiple consecutive wins (along with an emote to rub it in everyone's face) it seemed like just enough to cause us all to start getting frustrated and screw up team morale.