And yet Seinfield wasn’t pulled from the air in syndication after Kramers breakdown on stage
Kramer didn't insult Valerie Jarrett.
It wasn't what Roseanne Barr Tweeted, it was who she mocked. Had she said the same thing about Maxine Waters, she'd still have a job (after some minor scolding). Not Valerie Jarrett. She's still too powerful.
I can't say for certain what would have happened if Jerry Seinfeld twittered something people thought was racist -- his liberal politics would probably protect him -- but nobody was going to stop the reruns because of anything Kramer or Newman or the Soup Nazi or Tim Whatley or David Puddy or J. Peterman wrote or said.
Because it was Jerry Seinfeld's show, not Michael Richards's show and Seinfeld had nothing to do with what Richards did. Regarding The Cosby Show and Roseanne, the show creator is whom the scandal is about.