[Conno]

There are several reasons it takes longer now than it did then: construction standards have changed, health and safety laws have changed, and the technology being used for the new rides in these new constructions is far more complex.

Also consider that when they were initially building WDW - they didn't have to account for hundreds of thousands of visitors on property at any one time.

I'm still not sure why it takes as long as it does - but I can understand why it takes longer than it did.