i think the difference is, as others stated, sea world needs the annual passholders now. WDW does not.
since the bad press, whether warranted or not, (topic for elsewhere not here) i believe their attendance is signficiantly down. they need to get attendance up.
not only for the price of the admission tickets sold, and the food/beverage while there, but to make the park look active. people go to an empty park and say to themselves, there must be something wrong with this place, no one comes. even if it is subconscious it clicks.
WDW has more guests than they can handle and wants to decrease the crowds by decreasing APs. once they have the new attractions up and running and can handle more capacity, they may need the APs back. that is yet to be seen, if the new lands bring in enough guests to still fill the place, the APs will still be on the back burner. IMHO