I think the beach and pool are two separate issues. The beach is a part of the common open area of the resort and for everyone to enjoy. Disney encourages guests to explore the resort areas--of course they're hoping you find the gift shop or a reason to return.
The pools are for guests of that resort. It is an amenity, the guests pay for.
DVC members have the option to pool hop because it sounds cool and is a little used perk, and in a vague way DVC members are buying into WDW as a whole.
I can see the appeal of taking a few minutes on a hot day to sneak out of the parks and take a dip in a near-by pool, but it is technically not allowed. I believe Disney's enforcement varies by design. What is a huge problem in July is probably not even noticed in December.
I know if guests complain the offenders will always be asked to leave.
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