Due to the downturn in the economy here in the US, the dollar is weak and basically, the US is the international tourist destination of choice because, it's cheap! This is great that we are gather so many foreign dollars to help pump up lagging US sales, but at the same time, all of those folks, well, their diet is different than ours. While here in the US meat and potatoes had been king for many years, even the US diet is changing. So, with all of those guests with decreased demand on the supply of beef at the restaurants, it does make sense that they would decrease the offering of an expensive cut, like the tenderloin/filet, to just a few restaurants.
There is no need in supplying a bunch of restaurants with say 100 filets/night when they are only going through 20 and then wasting all of that meat and losing all of that profit. On top of that, the profit margin is probably reduced due to the increase in operating costs due to the rising price of everything. It makes sense that they are going to concentrate their efforts to keep that profit in places where it makes sense. Not to mention that from a marketing perspective a "Steakhouse" restaurant is where most people would expect to find a higher quality cut of meat, like a filet, so limiting their availablity to those sorts of establishments makes more sense.
Not everyone is on the DDP. The cost of a filet is certainly not cheap. There are lots of locals that keep Disney restaurants busy too. While they may use those AP's for a nice day/night out and go to a restaurant on property, they are not necessarily, even with the DDE, going to go for a high dollar filet. There are plenty of other more budget friendly menu options available. Again, this decreases the need for supply and shows a deminished demand for product. Add to this the need to control the "damage" of
free dining's bottom line, and it's not hard to see why the filet is going to be missing for a couple of months, at the very least.
This is just my take on the situation. YMMV
