If Shanghai Disneyland and Universal Beijing can both be around 1000 acres, Orlando which is also the most visited tourist location in world can afford a larger size park. It would also help to have a huge park especially if this one is geared towards the toddler crew. I mean one of the biggest complaints are strollers meaning large walkways will be needed which take up space. Add in parades and etc which will add to non usable space for attractions.
Secondly, more space allows them to create fully formed lands rather than just the highlights. I.E a full blown castle for Hogwarts with the great hall, dungeons, forbidden forest, Quidditch pitch, and Hogsmeade rather than a small part of Hogsmeade, a in ride version of the forbidden forest and a small version of the castle.
In the long term, more space keeps the problem Universal currently faces from happening aka not having room to expand and then taking things out and losing capacity.