I have seen their backlot. And I've seen that they are running out of open space. The last bit of space that really wasn't used much at all was where FJ sits. The space between Ripsaw and River is used as a bone yard (obviously that stuff can easily be moved to a warehouse off site). But there isn't a whole lot of space you can easily move a pyro lock down area. Or two large support structures for the parade (not to mention you'd probably want to keep those buildings near the parade. Some offices can be moved off site, but most of the ones that it's practical for are already off site. Your offices for attractions, entrance ops, security, food, merchandise, events and entertainment really shouldn't be moved off site. Your rehearsal rooms, warm up rooms and costume storage can't really be moved off site. There are huge warehouses off site, but there still needs to be a certain amount of storage onsite for food and merchandise. Tech services needs a lot of space to properly maintain all of those rides, the vehicles, and the buildings.
On the practical end there's a whole lot that goes into the operation of the theme parks that's a lot rougher then roller coaster tycoon's demo and build method.