There's a few things going on right now that you may not be aware of:
1) Disney is holding a large amount of tables back, out of the system, in preparation for CP Packages. This is probably the largest availability limiter to date.
2) The new online website has a lot of bugs and issues and it's causing some slots to become locked up in limbo. (There was someone today dealing with just that). I'm sure there's more of these slots going unreported as well (by non-DISers).
3) With ADRs at 190 days (for the time being, more than likely unintentional) a lot of high demand places are being swept up even faster than normal. (
Note: before someone says it... no, it is currently not 180+10, but a flat out 190. More than likely due to a glitch/bug in the resort validation piece of the v2 website See the Reservations board for a big long thread all about it including instructions as well as speculation and discussion on whether it's intended or not).
EDIT
I forgot to mention that chances are, some people are double-booking. It's been going on since at least the V1 site was launched, and I'd guess even before then. It may have become more popular when online ADRs were released, but I wouldn't think that it's a recent thing.
/EDIT
When did the online system start? I love it, but I hate how little is available. Things like WCC are filling up on some days. That's just nuts!
The original online system started last June. The website was recently updated (mid-May I think, maybe early May) to what I have dubbed "v2" (or "Version 2").
I just hope these people are kind enough to cancel the reservation they won't use! Even September, a relatively slow month, has very few ADRs left!
September has been slow in the park attendance department, however, restaurants have typically been packed from my experience as well as several others around the boards. I know last year in Sept, it was a struggle to get most of my ADRs done right at 6am on my 90th day (it was 90 days last year).