I've heard that since BLT was built, the GF is now among the last to fill.
If they also convert some of the existing GF rooms to
DVC, this will help their hotel division as well. Reduced deluxe rooms supply means Disney can reduce the discounts during low demand years. During high demand years, they raise the hotel pricing. Additionally, it spreads resort expenses out between DVC MFs and the hotel.
From a business perspective, VGF makes a lot of sense for Disney.