Here we go again. It seems like no matter how many times we shoot this zombie idea in the head, it just keeps coming back. One more try:
APS-C far outsells full frame. Full frame remains a niche market in the DSLR world, not the dominant format.
There is a substantial cost barrier to entry with even the "bargain" full frame cameras now being announced. To purchase the lowest cost full frame camera with any lens that can take advantage of the larger format requires an investment of about $2,500 minimum. That is cost prohibitive not only for casual photographers, but for many, if not most, enthusiasts as well.
The APS-C genie is out of the bottle and it's unlikely either Canon or Nikon can put it back in. Serious APS-C enthusiasts prefer the format for a variety of reasons, probably the biggest being the extra reach the format offers for telephoto lenses.
The success of both the 7D and the 60D demonstrates that there is a solid market for higher end APS-C cameras. Neither Canon nor Nikon can afford to leave these customers on the table.
With the current state of technology, alternatives remain inferior. That includes both in-camera cropping of a larger sensor and mirrorless EVFs. While this may change in the future, the future isn't here yet.
The truth is, not even Canon and Nikon know where the market is headed. As responsible, well-managed companies, they are trying to position themselves to take advantage of whatever direction the market goes, but they can't predict or direct the market over any long term.
What they do know is that the bottom has fallen out of the formerly lucrative point and shoot market, thanks to cell phone competition. They know that enthusiasts are a coveted segment because they have disposable income and are willing to spend it. So, all of the companies are trying to offer a variety of products that will appeal to those highly desired consumers who are willing to part with substantial amounts of money for their hobby.
Too many people are confusing the decision to offer a lower cost full frame body with a guaranteed demand for the product. The truth is, camera manufacturers think there is a demand based on market research, but they won't really know that for a year or two, after they have seen and studied the actual results. In the meantime, they are certainly not going to sacrifice a proven segment of the market. Such an irresponsible gamble with shareholders' money carries risks that no conscientious executive would take.