well, as they seem to cut corners everywhere else, it could be the difference of Virgin Premium unleaded and TCD City Unleaded

(yes, I know they run on parrafin!)
the average Virgin flyer is not going to be looking at the possibility of 24 hour delays due to lack of available aircraft either, plus those of us with children under 3 can go Upper class wheras the cheap (in all senses of the word) TCD sunshine first they cannot, (and even worse in Sunshine premium with a 6 year old limit, isnt WDW for children???) plus 3 X 32 Kg of luggage against a "huge" 40Kg luggage allowance on TCD, no clubhouse, the list goes on.
Oh, and the big fact of course, Virgin fly every day AND you can fly for however many days you want, not be restricted to 7. 14 or 21 days only