The extreme shit they post and hostility towards anyone who isn't as bitter, vindictive and hateful as them are some of the reasons why incels are hated and shunned.
Theyโre shunned cause of their looks. Like how anime got popular among black people here in the US because attractive people starting talking about it
I suppose by definition the word brings about an image of a dejected, lonely, hateful, toxic young man, so it's probably that. Anyone who chooses to directly identify themselves with inceldom probably isn't a very agreeable, pleasant person.