On a side note, it's more than just staffing. The Saturday and Sunday after Thanksgiving tend to be extremely busy days as a high number of guests leave for home after the holiday. Even with a full complement of housekeepers, inspectors, engineers, and housekeeping attendants, such a barrage of guests leaving requires a superhuman effort. Among other things, CMs can't get into the rooms until guests leave, and many don't leave until right before 11 and often after. One housekeeper may be assigned four rooms, and if none leave until 10:30, 11, or even later, said housekeeper is already behind the power curve.
Another factor is the size of the room. Studios obviously take the least amount of time all things being equal. GVs and cabins take the most. A Grand Villa can take 4-5 hours easily, for example. If the prior guests don't pull out until, say, 11:15, then if a housekeeper gets into the GV right after...well, you get the picture. And, yes, if something goes wrong with the room--heating/cooling system, plumbing, appliance issues--then those have to be resolved first.
All that to say, sure, not getting your room by 4 p.m. (which is not exactly how
DVC words it) is annoying, aggravating. Yet, I can assure you, the CMs are taking the issue of getting you into your room seriously and working hard to get you there. No one wants a guest to have a bad experience at any time, much less at the beginning of his/her trip.