I have to echo the thoughts of some here - if the SEC didn't have such good and highly ranked teams, ESPN wouldn't be talking about them as much.
I'll bet because the SEC is doing well, that's the fanbases ESPN is targeting to get more eyeballs. Plus, several SEC teams right now are shaping the playoff picture and will be right in the thick of it all at the end of the season, so it's difficult not to talk about them.
As someone mentioned, if the B1G were just as good, we'd be getting probably double the coverage that we are. But, there aren't a lot of exciting story lines nationally with the B1G, where as the SEC will likely churn out the national champion.
I certainly think the SEC/ESPN relationship is one that comes with bias, but I don't think there's much when it comes to these graphs.