Disney hasn't explained it. There are a couple of theories, one more plausible than the other. The implausible? They're keeping an eye out for potential mass shooters and/or human traffickers by popping in once a day, not opening any drawers or looking in any bags, and popping right back out. Implausible for two reasons - one, it isn't going to catch anyone interested in hiding what they're doing and two, it is being applied without regard to the probability of a resort being used for either of those things (a mass shooter isn't going to have much success from the window of his ground-floor, lake-view room at CBR, and a human trafficker isn't going to pay $500+/night to use Poly as a base for profit-driven criminal activity). The plausible? Simple CYA strategy - if they don't do checks and something happens they could be sued, so they preemptively instituted a policy aimed at proving they take security seriously.