You have to first think of HGVC properties as already sold and some "interest" in each unit is owned by an individual(s). The way timeshares work, or timeshare theory, is that you pay for some fraction of an ownership interest in a unit and then you either stay there based on your allocation or percentage, rent it out, or trade it.

When units go empty the resort will sell them on the open market and it's typically far less than what you'd pay at a full-service resort hotel. But therein lies the rub; they are not full service. They don't change your sheets every night. They don't leave chocolates on the bed. Their idea of room service is pizza delivery. These timeshare condos are really all about having the amenities and features of an apartment/condo, without all the overhead of a full-service hotel. It's a trade off.

if the resort is fully sold, meaning all interests in the units are sold, and everyone is up to date on "maintenance" fees, then the resort loses no money by having units go empty. To help offset some costs, and perhaps help an owner that chose not to use their unit, the resort can and will sell empty units as hotel rooms. In some cases, when rented as a hotel unit, the resort will provide traditional housekeeping services (daily). But still, no mint on the pillow.

At least that's my view as both a timeshare owner (Disney, Vacation Village) and a traveler that is in a hotel 1/3rd of the year.