When sailing, you more or less choose your angle of heel (subject to trade offs of speed and heading). In any kind of respectable wind you do not “slosh”, the angle of heel affects the effective area of the sail to the wind and forms a sort of stabilizing feedback loop. You go up and down over the waves, and sometimes have a lateral oscillation across them, but rolling is minimal.

Now, once you anchor, if there are waves coming from a direction other than the bow (because they refract around whatever is sheltering you), and those waves are roughly the natural period of oscillation of your boat’s roll… then you get things flying out of cabinets and trying to sleep while clinging to your bunk. Scaling up to a mega yacht makes your roll period long enough that it isn’t so much of a problem.

All that said, I’m sure they have tanks for the pool water, since it is probably fresh water.

They have stabilisers to stop them rolling side to side