Jesus, you really don't get it. A touch for a RB is not the same as a catch is for a WR, which is not the same as a pass attempt for a QB. In order for a WR to make a catch he has to do something positive first. He has to get open and he has to catch the ball. Therefore the catch itself is a positive for a WR. On the other hand a RB does nothing inherently positive to get a carry and
a QB does nothing inherently positive to get a pass attempt.
By the way TDs per touch isn't relevant at all for a RB either. Their TD totals are widely dependent on where they get their carries on the field. Sort of why Trent Richardson was a turd even while having 11 rushing TDs in a season.