(This is not meant to sound mean.) You asked HOW they do so many cruises - then said money didn’t matter. For some, this is the case.
But notice the majority of the responses talk about sailing with discounts (FL, military…), looking for lower priced cruises, sailing outside school break.
To answer your explicit question, No, Disney has no discount for booking B2B or multiple cruises in a year. And no discount for loyalty, like Royal or MSC has.
Bottom line, they just make the
choice to spend their money and vacation time (or are not having to show up at an office) on a cruise. Sort of like your 4-5 trips to WDW in a year. And some of these cruisers are also doing WDW trips, too. All rather mind-blowing. (No, I am not pointing fingers. I did a B2B 25 night combo; then had to fly home from Europe. Had some 5-cruise years. I have spent 188 nights cruising various cruise lines. I consider myself very fortunate). I am also short enough to not need a Verandah (Only 5’9”)