In the move to RT on ARM, MS had to say screw it to #2 and #3 and the move to a tablet forced them to say screw it to #1, too. "Desktop Windows" on a tablet has been shown not to work time and time again. Hell, the move to to a tablet essentially removes #2 and #3 since most programs are shit if they aren't designed specifically for a tablet.
#2 and #3 were never really under MS control, either. MS hoped to follow the "build it and they will come" philosophy. It worked with iOS and Android, but I guess people are just too tired to go another step, MS/ARM/RT is horrible to program for or they carry enough of a grudge that they just won't.
So why, or rather when, would I buy an RT tablet? When it's cheap. Just like any other tablet, it'll do about 90% of what I need it to do, regardless of the OS.