There's been quite a bit of research regarding the randomness of turnovers, and the studies indicate that around 55% of turnovers are explained by luck.
That still leaves 45% of turnovers explained by something else - defensive player skill and QB accuracy are big ones. I'm not sure if much can be attributed to coaching. You can draw up more blitzes and do tip drills and strip drills, but it's hard to coach turnovers.
In Nebraska's case, I'm sure playing from behind isn't helping. The NU offense has to to take more risks while opposing offenses can get more conservative.
A good example is:
2003 = 47 Turnovers by Husker defense - Bo hailed as defensive genius.
The rest of the story:
2008 = 17
2009 = 28
2010 = 23
2011 = 18
2012 = 23
2013 = 18
2014 = 23