For one thing, interfering with the free market is a fools errand.
Let’s say the top 15 RB’s went on strike. Then 15 GM’s each make a phone call to an unemployed RB that’s 90% of the striking RB’s in terms of talent and hire him on a game by game basis for the prevailing RB rate. Problem solved from pov of teams and fans and TV. Top RB’s are soon largely forgotten and lose far more money than they can ever regain. Everybody wins except the ‘top RB’s.
The Law of Supply and Demand is kinda like the Law of Gravity. They’re both tough to beat.
