Because it's an alt.
And it's supposed to troll and harass users.
If it's naming a user, it's making it "less fun" for the user to remain on the site.
Which is violating the TOS.
So yes, I have banned alts with such names from posting and commenting,
cuz we can't have anything of the kind written on your screen,
no matter if it's in a comment section or username.