It's because it does not really cost them more to enable 3D in new sets they sell. The big expense is the glasses which they sell seperately anyways.
My oldest son works in the studios in LA, his story is they don't do anything that is not expected to make money. Profit is the game, so again, somebody is buying this stuff or they, (the studios and the equipment manufactures) would not be messing with it. Yea I know 3D will be gone it a year of two......I wouldn't bet the house on it.
As anything the glasses will get cheaper or not be needed in future generations; Hell I can remember a "VTR" (video tape recorder) was selling for a 1000 bucks, tapes were 50 bucks. Within a couple of years the "VCR" (video cassette recorder) was under 500 dollars.
HD TV's were once 10K and there was no HD or very limited examples.
I know a guy who thinks HD is a myth, says he can't tell the difference, and he's Harvard educated.....As always the market sorts this stuff out. 3D has targeted a very specific market that is interested in anything new to them, (the programming speaks for itself).