It's not about how much skill is required to do something.
It's about how well you can do a defined element.
Yeah, I'm sure doing a triple back-flip requires more skill than doing a quad,
but you ain't gonna get any points for it.
If you legitimize UR as you suggest and give in-between points,
skaters who are not quite capable of clean triple jumps or 3-3 combo will be practicing under-rotation and doing them on purpose in competition.
Do they/we/you really want to see that?
Besides, are you going to give same points to a jump with 2.6 rotations as a jump with 2.4 rotations? How about 2.2?
IAGH (it ain't gonna happen).
Figure skating jumps are well-defined moves.
Either you do a triple, or do a double. Not something in between.
It should never be "jump up, and rotate as much as you can!"