Because it doesn't work basically. All Bluray Disks are encoded in 24hz, meaning that you need a TV and a Bluray player that can display a signal in 24hz or a multiple of it, or you get noticeable 'judder' when there is a pan shot, like the movie is sticking. As of right now, it's really only projectors that can display them properly, and having spent £600 on a TV, £300 on a PS3 and £250 on a surround sound kit, I don't feel I should have to pay out extra.
They're essentially something that is already broken, and although Sony could patch the PS3 to convert 24hz, they haven't in the 3 years the console has been out, so they probably never will. Sky HD on the other hand, cost me £60 a month, and displays everything in 50hz. The picture difference is immense. I have Inception on Bluray, but I still paid out to get it from box office when I watched it for the first time because I knew the picture problems from the Bluray would ruin my enjoyment of the film.
