Why do I give even a second thought to the reaction of other online users (who may not even be human) when I get blocked? They’re strangers. None of this matters. It will not affect my physical life in any way what so ever. My rational side is absolutely boggled at my emotional side. (additionally, I know I’m not the only one but I prefer to ask questions like this in first person.)
The reaction probably comes because rejection, being ignored, and/or ostracised are perceived as real injury by your brain.
Anger typically comes from fear, and the threat of ostracisation is an existential threat for the typical human brain.
We evolved as social beings, social injury and threat works the same as other types.