I'll just give a few examples...Fortress Explorations, here is a place that has a lot of little hidden rooms and corridors and stairs everywhere. From what I recall I saw one elevator. Now consider how many tons of strollers and ECV's you see in WDW and consider what kind of complaints Disney would receive because they can't get to those areas. It would be a throughput disaster.
On the same subject, most of Fortress Explorations is not marked for dummies, so you actually have to....EXPLORE to see what is there. Yes, there are maps if you know where to look or a CM gives one to you, but I've noticed that guests are usually totally lost unless there's big signs everywhere.
Another reason I think is how much access there is, like on the SS Columbia and the other ship in front of Fortress Explorations (Renaissance?) I just have a feeling that those parts would be off-limits because guests would be doing damage or doing things I've seen guests in WDW do that I'd never expect from Japanese guests. There are a lot of nice props in the Renaissance Ship that are behind ropes or barriers, but those wouldn't last.
Although it's not a Disney park, I remember at IOA when Spiderman first opened, they had the office area which had these props in grey paint that had some fruit and a toaster, etc. There was also these computers and various props. In a very short time, they were pretty beaten up.
So Disney could do a lot of upkeep to make up for it, but I doubt they'd put the same effort as OLC does.
Those are just some things I thought about while there.