In many hotel programs, hotels don't get paid anywhere near the normal paid stay rate for points redemptions. Some get a tiny fraction of that (perhaps about $20 per night when the room rate would have been about $100, for example?), unless the hotel is very close to fully booked perhaps (in which case the hotel program may pay the property significantly more on the same points redemption stay . So while the hotels have to honor that ultralow rate (from the hotel program) if the guest shows up, is it any surprise that they don't want to honor this ultralow rate when the guest doesn't show up? The contract is probably written in such a way that they only get reimbursed at all when the guest checks in, so a completely other mechanism for getting paid is necessary if the guest doesn't show up.

Meanwhile, the contracts between each hotel program and its franchisees is going to be different that for the next hotel program and its franchisees, so it's not a surprise that these policies may be somewhat different from one hotel program to another.

The reason the hotel program will not explain the reasons to you is most likely because the exact reasons are buried in private contracts between the hotel program and its franchisees, and why should you get access to such private contracts just because they're the only thing than can explain the reasons for such policies?

The miles and points words is filled with lots of different policies for which the reasons are never explained. This is far from the only policy for which the reason is not stated.