I don’t think you really understand what professors make already. Even a CS professor at UCLA is barely breaking $100k, and they would be in dire straights for their market if the university didn’t back their housing loan. Sometimes professors have the option of topping up their salary out of their research grants, but that has a few problems in itself.
It's a little tough to generalize about salary in academia.
Obviously, a 'professor' covers multiple ranks in the academic hierarchy, but if you look at the published pay scales for assistant professors (I believe the lowest professor ranking with tenure) at University of California, it looks like large majority of them are breaking $100k [1]. I don't see a way of breaking those results into discipline, I'd imagine that those individuals in fields like CS vs. more academia-exclusive fields like literature or geography (relatively, anyway) are making towards the higher scale of that. Some of them in with clearly medical-related title are making much more, but I think that's to be expected.
Also, it's possible I'm mistaken, but I believe professors are allowed to be paid to act as advisors or "resources" for external organizations to act as a secondary revenue stream? Combined with topping off their salary with research grants as you pointed out, and the nice perks academia offers if you can get tenure (job security, etc.), I'm not sure that even this data fully encapsulates compensation either way
AFAIK an assistant professor typically is on the tenure track, but doesn't have it yet (= they'll get tenure if they meet certain goals during this time)
Ah, you're correct. I was thinking about associate professorship, which it looks like is usually accompanied by tenure. Sorry, I sometimes get a little mixed up between which one of those is on the tenured/non-tenured side of things.
