The tough part is that I struggle to see a scenario where this market swings back positive. There is a constant supply of talented RBs from the collegiate ranks, and the NFL is going to continue to encourage rule enforcement that allows for more passing and high-flying offenses.

It sounds unethical but if I was a GM, I would run a tandem of cheap RBs, and once the rookie contract was up, I would tag one and plan to draft another in the second round. Rinse and repeat.

This is a microcosm of how employment works in the world at large.

You aren't paid based upon how difficult your job is, nor are you paid strictly based on how much value you add. You're paid based on a function of value added, AND how replaceable you are. Essentially supply vs demand. If your job is hard and you add a ton of value, but you're easily replaceable, then you won't make much money. There's just too much supply. It doesn't matter that RBs are important if you can just throw a rock and hit someone who can fill the role.

Likewise if you're difficult to replace, but don't add a ton of value you also won't make a lot of money. My best guess for an example of this would be long snappers.