Comment by ghaff

Yes. Exactly.

There are a bunch of reputational benefits to certain types of book writing which (probably) lead to significant career/comp benefits. But the direct money can be less than what companies will pay for a ghostwritten content marketing-type blog. Or even whatever a lot of salaried people earn for doing that sort of work on company time. There's a reason a lot of "creatives" end up working for corporate product companies as their day job.