In the case of Kricfalusi, he first approached these girls when they were much younger - pubescent. He used his authority to pressure them into relationships (they worked for him!). The interest was not reciprocated. This appears to be a repeated behavior pattern. It's super super creepy.
I hadn't heard of the Seinfeld thing, so I looked it up. The girl turned 18 shortly after they met. She did not depend on him for his career. His other partners have been age-appropriate. Most importantly, she doesn't appear to be aggrieved, unlike Kricfalusi's victims.
Seinfeld's relationship age difference is eyebrow-raising and maybe a bit cringeworthy, but not inherently damning. Even young adult human beings have agency.
Probably the big difference with Seinfeld is one or more of the following:
1. The age of consent in New York is 17, so there was nothing illegal about it.
2. She turned 18 shortly after they met. Seinfeld claims that all they did together before she turned 18 was go out to eat. The actual dating started after she was 18.
3. He wasn't doing anything to hide the relationship from the public or from her parents.
4. It doesn't appear that he used any power or leverage to coerce her into a relationship. It's unclear if she even knew who he was when he asked for and received her phone number during their first meeting, which was a chance encounter in Central Park.
I was not previously familiar with Seinfeld's relationship with a much younger woman, but a quick search indicates they dated for a few years while she was in college and then the relationship ended. She apparently turned down his marriage proposal.
She has apparently not come forward to suggest that he was mistreating her. If she did, that story would likely get plenty of press. People apparently gave him a hard time about the relationship at the time.
We aren't frying Seinfeld because his much younger ex girlfriend isn't accusing him. Ultimately, her opinion here carries more weight than that of the rest of the world. Whatever people may think of the inappropriateness of the age difference, as far as I know, she is not claiming she was victimized.
Meanwhile, established religious groups marry young teenage girls, sometimes several of them at once.
Not sure if the "pre-calculated thing" can be substantiated though.
If the other situations involving abusive men of the last year or so are any guide, there are others who haven't come forward, for whatever reason.