RB's need to be able to pick up complicated blitz schemes or your QB gets killed. If you can't master blocking, you aren't going to play. Because defenses can easily run blitz a one-dimensional RB when he's in.
To digress, fans always want to play the shiny new object, and think that their own coaches are in cahoots to sabotage their program and their very own jobs and their family's wellbeing. If a RB can't read a blitz, he's not playing. If a LB can't pick ups his reads and step in the right direction, he's not playing. Coaches spend months on the practice field coaching and evaluating. Occam's Razor.