It means he lacks the ability to reinvent his comedy to fit the times. Instead he just complains.

We all need to continue to reinvent ourselves over time. Things change. We need to retool for the times ahead. Reality is Seinfeld doesn’t need to because he already made his money.

So instead of him getting back on the horse he just sits back and complains like the out of touch old turd that he is. He sucks but just can’t accept it or admit it. It’s easier to whine.

He is a has-been and never will be again.