Good question, hoosier pride. White RB's are always very popular with the fans. I can remember several white RB's that had entire stadiums chanting their names during games in almost surreal events. ie - the chant of "Hoover" from the Carolina crowd, "Alstott" from Purdue and Tampa fans, "Eckel" just last year during Navy games, "Brewer" from South Carolina fans at the Outback Bowl a few years ago, and many others that don't come to mind right now. These are just the games that I happened to catch on TV. I'm sure there are many other examples that I have missed.
Yes, white running backs would be a great marketing tool. So why isn't the NFL marketing white running backs? Maybe it's just to easy for teams to make money these days. The fans seem to show-up no matter what, jerseys seem to be sold no matter what disgraceful black athlete's name is printed on the back, and black football icons are hyped by the media 24/7 no matter what white fans really crave (the white icon).
In the end we have to blame the fans for not being knowledgable of what they are endorsing. We need a more educated fan-base throughout the country. The word has to get out to support white athletes. That's what this site is about. With more and more people reading this site and sites like this maybe things will begin to change in time.