As long as they keep cramming the guests in for the next few years, TDO are happy. They've managed to convince thousands of people to pre-pay 45 years worth of vacations, and all those DVC members, despite evidence to the contrary, seem to think the the quality and standards of the parks are going to stay the same or improve over that time.
If Disney lets the parks decline, if they don't build much that's new and cheapen what's already they're, to the point where the DVC owners don't want to come every year anymore, who cares? They have your money now. You said you wanted to come to Disney for 45 years... be careful what you wish for. The WDW of 2035 is likely to be very different to what we have today, so it makes sense to build DVC fast and sell them up before people notice that theme park investment has stagnated.