This type of behavior has been a problem with
Disney vacations (be it cruises or WDW) for a long time. You used to see it with WDW all the time. People would book tons of ADRs for restaurants - in some cases, one in each park for each day of their trip - and unfortunately wouldn't even have the decency to cancel the ones they weren't using. Now, some of the blame for that was the ridiculous 180-window they used to have. However, still didn't justify the behavior. This forced Disney to implement the no-show fees and other measures.
I mentioned in another thread, regarding unique itineraries like Panama Canal cruises, about how so many of the Pearl and Platinum people book the rooms opening day even though they know there is little to no chance they will actually go on that cruise - driving up prices and "selling out" the sailing by the time it opens to the general public (or possibly even Silver CC members) only to have plenty of rooms open up later. Same thing happens with Cabanas, Mixology, & Palo brunch (although those have very fewer cancellations). A lot of times people do these things "just in case" - because they can, without penalty of any sort. Make the deposit non-refundable on the "special" itineraries, and cabana bookings. Behaviors will change.
You could say one big difference between the WDW restaurants reservations and
DCL stuff is that with the restaurants, those tables ended up sitting empty and costing Disney revenue. Whereas, with DCL, when someone cancels a cabana, Palo brunch, a Mixology spot (because you will be charged for it if you don't), it is probably scooped up with by someone else rather quickly. It's never going to sit empty.