Running backs have a hard life. They tend to age poorly and, as a result, they tend to miss the big payday of a second contract. There also tends to be an ample supply of average-ish running backs available, and while you might not be able to randomly find a Barry Sanders, you can often find Dorsey Levens (5th round) or Ryan Grant (undrafted) or Samkon Gado (undrafted) or James Starks (6th round) or Aaron Jones (5th round) without too much trouble. Heck, Ahman Green was a 3rd rounder.
There are likely to be quite a few good, productive running backs in this class, with the NFL Mock Draft Database consensus board currently projecting 22 will be drafted, starting with Jonathan Brooks of Texas and finishing up with Georgia’s Kendall Milton.