Let's separate the two issues.
While I certainly don't agree with insisting someone sign such a contract (and I haven't seen any of that myself on Facebook, where I hang out a lot), any author who signs such a contract without first questioning its content, and asking advice from others, is a dimwit. All one has to do is hang out on social media for a few hours, talking to authors from across the spectrum, and one will quickly and easily see that such contract terms are not the norm, and will gain you, as an author, absolutely nothing.
As far as teaching classes and workshops, yes, there are authors making money from teaching others what they've learned through hard work plus trial and error. I see nothing wrong or predatory about this, to be honest. I've learned most of the things I know about this industry from others, though I haven't paid for all of that knowledge. But I have no qualms about paying someone a reasonable amount of money to teach a class in specifics. Things I've chosen to learn more about from someone who has been there, done that, and made it work for him or her. It's no different than in any other field where people pay to attend workshops or continuing education classes. Why should it be considered predatory for authors to do it?
Some behaviors I have seen are authors who toot their own "I can teach this better than anyone else can!" horn all over social media, even going so far as to name names and call out other authors who teach the same kinds of classes. They tell everyone who will listen why those other authors aren't worth the time or money. Now that, to me, is worse than high school mean girls behavior, and I'd simply avoid those pompous, silly people like the plague.
And I don't know. Maybe not everyone has been around the block enough to be able to discern that kind of cult-like "I'm better than SHE is" nonsense from the legit authors who are simply trying to pass on the knowledge they've gained, and make a few bucks doing so along the way. As I said, I see nothing wrong with the latter. The former, well, like I also said, I'd simply avoid. And I'd also laugh at them for being such immature brats. LOL!!