The caption explains a lot. It seems these aren’t necessarily the full service luxury hotels with the fully staffed reception and bell service 24 hours a day. These seem to be time shares which are glorified condos. I have stayed at these before. While they are nice, there is not the level of service that you get at a full service hotel. For example, There is no bellman, instead they provide trolleys for you to being up your own luggage. The cleaning staff only come between stays, the reception desk is only open during business hours, etc.
Given this, a lot more stuff make sense. It would be trivial to load up a trolley with the mattress and take it where you want it. At night, there is not a lot of people around so it would be easy. The cleaning staff don’t come everyday so it would be be some time before the missing mattress was noticed.