DVCOwner
A Long Time DVC Member
@Master Yoda was on the right track, but I'll modify his answer slightly. Wall Street doesn't really care about how long it takes to complete individual projects, they care about capital spending in total. It's also a mistake to assume they want to see small capital expenditures. What they really care about most is that capital expenditures are relatively smooth. In other words, they like to see steady, robust investments in capital assets. They do not want to see peaks and valleys of huge spending followed by inactivity. Predictability good, volatility bad.
With that in mind, it's easy to see why long projects that overlap here and there are more attractive than quick-burst projects that are banged out quickly. The Disney Dream gave way to the DCA relaunch and Cars Land, which gave way to the Disney Fantasy (with MM+ going along the whole time in the background), which gave way to New Fantasyland, which gave way to Avatar (with Shanghai going on the whole time in the background), which will give way to Star Wars, which...
It's always better to have a revolving list of ongoing projects. As projects wrap up, others are beginning, and the cycle continues.
If I could add to this only one thing. There is also a point of the project costing more if spread out to far, so the job is managing your capital investment with increasing the cost be doing construction to fast or to slow.
A lot of people have complained about the cost of Avatar, but looking at the photos I think the cost is in the details. In this case the rock work. You could build these two rides much cheaper of you are not concerned with the details. Details cost money. Just as if you are building a home and you start adding crown molding, chair rails, hard wood flooring, granite tops, etc. You can build a house a lot cheaper if you are not worried about the details.