From my observations here, I think there are definitely owners, including some folks who regularly participate on TUG, whose pattern of rental activity could easily be considered commercial use. It's a subjective determination, but there are at least a handful of folks here that I suspect to be clearly on the "wrong" side of that line.
The question is whether MVC is actually trying to crack down on or seriously dissuade these uses, or whether they are just trying to check a box (literally, in some cases) so that they can claim to be upholding the requirements in the CC&Rs.
Asking people to self-certify ("I promise this isn't a commercial use") is probably a pretty ineffective enforcement technique, but it would let MVC say that they do not allow commercial uses (because if anyone admits to them, then they are disallowed.) Nobody admits to them, so MVC, with blinders on, says "it's not happening."
It still isn't clear to me whether they actually have a business reason to discourage people like the quasi-commercial owners here on TUG from continuing to do their thing. I suppose if there's enough people doing it, then it impacts availability (especially at peak times) for the "normal" owners which hurts both sales to and retention of owners. If that problem is severe enough, it might motivate them to do something about it.
I'm intentionally not naming names here, because it doesn't matter and I'm not trying to shame or label anyone. But if you've ever thought of your rental activity as being a business, even MAYBE a commercial use, then it probably is... or could be seen that way by someone like MVC.
The other factor that would come into play if they actually started cracking down and cancelling reservations of "commercial" users, is that certainly Vistana/Starwood sales, and probably MVC too, has actively touted the ability to rent out what you own to encourage people to buy. So they may have a concern about their ability to start actively restricting a use which they themselves encouraged people to spend their money to enable. I'm a very occasional renter of my ownerships – maybe 10% of the time – but that ability was promoted by Sales and at least one of my purchases was kind of based on/justified by that possibility. As it turned out, I like using that property more than I like renting it, so I haven't rented it much. But I'd be pretty unhappy if my ability to rent it when I want to was curtailed.