It may sound simpler to have them both end at the same time, but that would not be the case.
When the
DVC resort closes down, it will have to be fully refurbished at the least, and possibly re-themed or even rebuilt in parts. They may even have some add-ons to build new before they can start selling it as a new DVC resort. It will be a major construction project and very expensive.
If Poly1 and Poly2 have to go through this at the same time, there would be TWO major construction projects, on BOTH SIDES of the Polynesian Village Resort. Can you imagine the problems and complaints from that?
Having both construction projects going on at the same time would at least double the costs, if not more, and cause the loss of revenue from both sides at the same time. It also may require the closure of both the quiet pool near Poly1 and the new pool at Poly2. What a mess that would be.
If, however, they are separated by even a small number of years, Poly1 could be closed down and go through all of this while Poly2 is still up and running, providing revenue as well as it's pool, dining, and other services for the Polynesian guests. Then, when its Poly2's turn, the new Poly1 will be up and running and fully available to the Polynesian guests.
While we all know that DVC can be a bit short-sited on some of their decisions, I don't see them purposefully deciding that having major construction projects on both sides of the Poly at the same time is in
their best interests.
.