Another key factor .. Is any time when the co. tries to shoehorn new attractions into old facilities. Thus ... requiring lots of time put into refitting the building to a new purpose.
This happened with Country Bear Jamboree in Disneyland ... which became the Pooh attraction. Both theaters had raked floors. Well, that had to be level. The attraction cost some 30-35 million in 2002/03 dollars ... I bet a good chunk of that went into refitting the old building. And took plenty of time - vs. tearing it down, and having a clean slate to work with.
Same thing for Buzz Lightyear. That was a tight fit into the former Circle-Vision space.
If, in future projects .. that entail recycling old attractions to make new ones ... seems to take longer.
This is where I'm glad much of DCA 2.0 worked with clean slates - Carsland have nothing to re-work with. Golden Dreams theater completely knocked-down for Little Mermaid ... and Buena Vista Street .. mostly new construction.
I hope a future Tomorrowland involves "clean slates". The less they re-work .. the less time I think it would take to remodel the land. IF we ever get to see it happen.