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 protagon

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.