Disney is responsible for the difficulties of decreased availability at 7 months.
1. The online program makes it very easy for people to book and use their points. And they do. This is actually a good thing.
2. The program makes it easier for people to rent out their points when they aren't going to use them. This means that points get used and take up reservations, instead of expiring. However, another part of this is that Disney has made it very attractive to rent points out by raising the prices of rooms so very high. So, more points get used. If you have 50 points you are going to lose, but points only rent for $5 each then you stand to lose maybe $250. Not nice, but not a really big deal. But if points are going for $20 a point (and I have rented a lot of points at $20 a point) then your 50 points becomes $1000. That is much more significant!!!
3. Disney did establish a program in DVC that has some intrinsic value. Unlike most timeshares, where point value gradually goes to zero, the DVC points retain value, as long as they can be used to stay at the very expensive resorts that Disney has created by raising their prices. This makes it worthwhile for people to SELL their points on the RESALE market when they get tired of them, or too old for them, or their circumstances change. So, points that used to sit around doing nothing, now go into the hands of people (the resale buyers) who are more likely to use them.
4. HHI and Vero Beach owners who bought resale. This is a special sub category of resale buyers, not just because they bought contracts, and kept them active, but also because they are especially likely to shift from their Home Resort to use them at Disney World. The original owners of HHI and VB were likely to have purchased those locations because they LIKED those locations. But as the population has aged and changed and new resale buyers have come in, a very very large part of those resale buyers bought VB and HHI, with no intention to ever stay there, but because they were cheap, and it gave them an inexpensive way to stay at Disney World. This puts more pressure on the rest of the system.
5. Disney has sold too many small contracts. Contracts that only have enough points to stay in studios. So all the studios book up, and this then causes a cascade effect, forcing other people, who formerly stayed in studios, to use up their points by staying in other rooms, 1 bedroom and 2 bedroom units. These units were also more available in the past because the people using them formerly spent their points on studios.
6. Disney came up with the genius idea to designate certain units, Polynesian Bungalows in particular, but also others such as Copper Creek cabins, as "very high point reservoir units." In other words, make bungalows and cabins in order to create a lot of (inexpensive to build) points that Disney could sell. And they knew, or should have known that people would not choose to use their points so wastefully, on the Bungalows. Even better for Disney, they can now rent those out. Meanwhile the points that ARE NOT USED to stay in the bungalows go into the general pool and soak up other reservations at other places.
7. Disney made a mistake by building Aulani. I don't care how much Disney tries to put a rosy face on it and cherry pick their statistics to deny that Aulani people are actually staying at Disney world - the Aulani owners actually ARE staying at Disney World. Why? Because it costs less to fly to Orlando from EVERYWHERE in the continental United States (even the west coast), than to fly to Hawaii. Besides, Disney World is a whole lot more fun and interesting than Aulani. Just the fact that Aulani is still only about half sold out, AFTER ALL THESE YEARS, shows that people don't want to stay there. And the people who don't want to stay there includes the people who actually bought it. (I'm not talking about EVERYONE, but a significant percentage.) Disney should have known better.
8. Because it is getting harder to book, people ARE planning their vacations farther out, both in the 11 month window and in the 7 month window. They know that to get what they want, they MUST plan ahead, or they are likely to find themselves with poor options. This takes inventory out of the pool, earlier, and makes it nearly impossible to plan late notice vacations.
Am I missing any other major factors?
The fact is, even if people are only using 10% more of their points than they did in the past, this is enough to tip the balance and make it hard to get reservations with short notice. And, when you add up the points that formerly went unused, and the points being used because they are 'rentable,' and the points that are being switched to standard DVC units instead of being used on Bungalows, Aulani, HHI and VB, you will find a far greater increase in the number of people competing for the same reservations.
But we have always been able to find the reservations we wanted. This time was less lead time because of family changing plans. (Vacation planning is not always 100% in our control) But we were still able to start trying to book right at 7 months! NOT 5 1/2 
Lets be honest...the real problem is that we want a room with the murphy bed because my children are incapable of sharing a bed without nuclear war (11 year old bed hog!!) 
