The 11 month rule itself was chosen long ago when DVC started. It could just as well have been 12 months or 10 months or even less. When OKW opened the windows were actually 11 months for owners of OKW (called the Disney Vacation Club at the time) and 10 months for owners from other DVC resorts. But of course at the time there were no owners of other DVC resorts. By the time that event finally occurred, they changed it to 7 months, and it has been 11 for home resort and 7 for others ever since. It continues to be that way because it works well and DVD has no logical reason to change it.
Guests have long been able to book the regular Disney hotels more than 11 months out. I remember seeing a story that menitoned that reservations for New Years Eve, Dec 31,1999, started to be made as early as 1988. Though you may reserve far out, you cannot lock in price when booking more than a year out.
Officially, the DVC resorts cannot be booked by cash paying guests more than 11 months out. DVD retains ownership in a certain percentage of each resort which it can rent, and it gets other points to rent via members trading out, via foreclosures and via exercise of right of first refusal. However, according to the official documents, DVD, in reserving rooms using the ownership interests and points it has, is required to follow the same booking rules that DVC members must follow, i.e., it is not supposed to book at a home resort more than 11 months out.
That is what DVD is supposed to do. Whether it always does is subject to question. A couple years ago I believe I caught it trying to lock up rooms for rentals more than 11 months out. At exactly 11 months out I checked AKV for availability of a GV at Jambo starting the Saturday before Thanksgiving to the Saturday after Thanksgiving. Strangely, I found the Saturday through Tuesday open but the Wednesday and Thanksgiving Thursday were full for the Jambo GVs. That is impossible if someone is following the 11 month rule. The only way those dates could be filled exactly 11 months out from the Saturday before Thanksgiving, is for all the days from Sat through Tuesday to also be filled. I emailed Members Services and Member Satisfaction about the issue. I got the standard email that my email was received and they would get back to me. They never got back to me. I emailed again following up on the same question. They never got back to me on that one either. The next year I did not see the Jambo GVs disappear for those Thanksgiving dates before 11 months out.
As to the comment above that DVD is required by law to retain ownership of a portion of the resort, that is not actually correct but as a practicable matter it is correct. DVD was not legally required to retain any ownership interest, but it had to so it could exercise complete control over the resort, including requiring as part of the sale to members that the members agree to transfer to it their rights to vote on any proposals at board meetings or any issues concerning management of the resort.