Have owned BWV since 1997. Back then you could still get a room at 5 months out most of the year (preferred view as there was no boardwalk view booking category at the time). Owners never feared not getting the room they wanted, even standard view, as long as they booked any time before the 7 month window opened, except there was always a concern about Grand Villas.
A lot has obviously changed since then, but there are several reasons for the change, and rentals are likely a minor culprit if at all. Also, it is still fairly easy to get BWV pool/garden view even at 7 months out about 8 1/2 months of the year, from the Monday after marathon weekend in Jan to late Sep. Moreover, during that time even standard and boardwalk view studios and 2BRs can sometimes be had for up to a week at 7 months out, and those are generally open a month or more past the 11 month window even for holiday times. One bedrooms, including standard and boardwalk view, are invariably open during that time beyond the 7 month window. However, studios of any view (and resulting 2BRs) seldom last far past the 7 month window any more for much of that time, and that is something that has actually existed since SSR had about a year's worth of sales and has grown for the near park resorts exponentially with the additon of SSR, AKV, and other non-WDW resorts.
The key season of change has been late September to marathon weekend in January. Christmas, Dec 23 to Jan 1, was always a very high demand time, although it usually did not require booking exactly11 months out and you could wait up to half a month to a month past the 11 month window and still get what you wanted. The Tuesday through Friday of Thanksgiving week was also fairly high demand and those nights could disappear by 9 months out in the early 2000's. The massive changes for that last quarter of the year did not just occur in the last couple years but have actually been building up over many years with each year getting somewhat worse than the prior one.
The multiple reasons for the change include:
Food & Wine has expanded from a short event to a very long event. They also added a half marathon weekend to it. Halloween has gone from being something that occurred at Halloween to something that occurs Sep and Oct. Christmas season was something that started Thanksgiving and now begins early Nov. The points are low, mostly choice season. The weather is ideal. Thus it has all the trappings for being a very popular DVC time.
You now have many more BWV members who want that time. Many who bought when it was on sale from DVD in the late 1990's to early 2000's still own there and that population, which was tied to children's school schedules when purchasing, has now aged, is sans children, and can choose to go during that last quarter. Moreover, many of those owners can now opt for a studio when in years past they needed a 1BR or 2BR with the kids. That particular BWV population continues to grow annually
Disney sold many low point "add ons" at BWV over the years. The ease of selling and buying resales has grown tremendously since since 2,000 as the internet became the place where everyone could easily find and purchase resales. Resale purchasers were not bound to the Disney 160 point minimum purchase that existed in the early through mid-2000's and the resales of highest demand were always those with low points, 25 to 100, meaning those add-ons eventually created many new owners in additon to the owners that purchased them, and those new owners have points that are enough only for studios, and those points can be best used in low point point seasons, like most of the last quarter of the year.
Disney, beginning in late 2009, then took another major step that assured demand for BWV studios in the last quarter of the year, would become excessive. Disney was always getting back BWV points to sell either via foreclosures or exercising right of first refusal, and when reselling the points it could do so in any increment, not being bound to the owner's contract size for a sale. After the crash, Disney did away with the 160 point minimum for new purchasers and started selling minimums of 100 points and at times even as low as 50 points. Moreover, Disney went on a binge of price increases beginning in 2011 that has raised the price it was selling BWV by 60% (when inflation was less than 2% annually), thus causing even more new purchasers to buy only the 100 point minimum, limiting them to reserving studios.
Disney meanwhile has not reacted to the increase in demand by doing any point increases that would lower the demand for the last quarter, which would be accompanied by point decreases in the low demand spring and summer seasons so demand could increase for those.
Adding to the problem is that owners just know more now. Before January 2012, there was no online reservation system. Before that time, any higher demand in the last quarter was just something members learned of in passing from hearing other members mention once in a while that they had a problem during October or another time. Prior to that time, members mostly believed October and November were increasing in demand but probably no worse than the spring break months, which were thought to be high demand. In fact, most incorrectly believed that the hardest rooms to get, and the ones that always required booking exactly 11 months out, were Grand Villas. We now know Grand Villas, except at BWV, are usually easy to get at 7 months out during most of that mid-Jan to late Sep period. Most knew early December, Thanksgiving, and Christmas were very high demand times for which there could be issues if you did not reserve some things 11 months out, but also assumed the same for the Easter weeks, July 4 time, and Presidents' week. Since Jan 2012, we have learned that the entire last quarter is a very high demand quarter and it keeps getting worse. That growth in knowledge has contributed to members believing more and more that the only safe course is to reserve that time exactly 11 months out, particularly if seeking a standard or boardwalk view studio at BWV or other usual suspects such as BLT standard studios, AKV club level studios, AKV value studios, and VGF studios.
Thus, the current poblem with reservations in the last quarter of the year, including problems at 11 months out for standard or boardwalk view studios at BWV, is the result of several changes over the years. Renters might contribute a little but it is likely very little. If you want to blame someone, the major culprit is Disney. It created the events that entice people to go during the last quarter, sold low point add-ons which could be resold to persons who had no previous 160 point minimum of points, destroyed all realistic minimums by lowering the minimum points needed to 100 and at times 50 so that many new purchasers would not have enough points to get anything larger than a studio, and greedily raised the price of points 60% during a recession to assure more and more would purchase only the 100 point minimum, and has done nothing to change the points needed in that last quarter in comparison to other quarters.