If you're going through one of the brokers, they have to have the people with the availability to book at 11 months. Just because those services are there, doesn't mean that they have an infinite number of members with points for their "home" resort being the one you're looking to book.
Also, depending on what size room you're looking to get (studio, 1 bdrm, 2 bdrm, grand villa, etc) there are only so many of those rooms to start with. The bigger the room, the less of them there are and the quicker they're gonna go.
So, I understand why you're stressed about it. Also remember, that even if you use one of the rental sites, they don't necessarily guarantee anything. They can't stop a DVC member from being foreclosed on or something should your reservation go to that particular individual. They are just a middle man to help you get in contact with DVC members who use them to rent points.
If you were to own DVC, you would be solidly in control of the financial security of your DVC account. You would be able to book at 11 months (depending on room size and home resort) and as long as you have the points and the units are available, you'd be in.
So you may not be doing anything wrong. It just may be that whatever site you're using just doesn't have the renters to fit your needs.