And because he's kind of shit. Seriously, every skill he possesses, someone else is at least fifty times his superior. When you get right down to it, Punisher is basically a homeless man with a shotgun, the most street level of street level "heroes." The other heroes don't work with him because, by and large, he doesn't matter. And when they DO work with Punisher, it's only to let him pretend that he does.

The only way Punisher really works for me is as a satire of an NRA supporter's opinion of how crime works, where if you just shoot all the bad men, eventually, there will be no more bad men.