I believe a fact to consider is Disney has not started construction on a non-
DVC hotel since 9/11, and since that tims has actually converted parts of 2 Deluxe hotels to DVC (5th floor of AKV Jambo and Contemporary North wing into BLT)
In addition, Disney has sold land to outside parties for hotels (i.e. 4 Seasons)
If Disney believed they could make more money building and operating more hotels, I'm sure they would. The mouse is very good at making money. It appears that Disney mostly "just" owns hotels, not to make huge margins on the rooms, but to get people on property and spend more money in the parks.
DVC is a great way to get people on property, and because owners need to use it or loose it, it is a regular, consistant stream of guests for the parks. (unlike what happened immediately after 9/11 when hotels had very few guests)