The problem with Seinfeld is that they deliberately set out to make a show with unsympathetic characters whose central personality trait is that they care about no one but themselves. Basically, they're sociopaths. Carlin can be abrasive, but I don't think he's a sociopath.
Because I don't believe in mocking people for their personal shortcomings.
I also think a fundamental principle of good drama is that it should have a protagonist that you can root for even if they are flawed. (Frasier is a good example.) None of Seinfeld's characters had any redeeming qualities whatsoever.