I think several factors have dictated the atmosphere of the stadium in the last few years, specifically after 2010. It was dead in 2011 (save the Wisconsin game) for obvious reasons. The bowl ban in 2012 certainly put a damper on the gameday atmosphere that year as well. It didn't help that the schedule that year (and for the past several years) has been considerably weak due to the B1G's shortcomings and the weak non-conference schedule. In 2013 there few marquee games (Wisconsin and PSU), but a National Title still didn't really seem like it was within grasp until after the Michigan game, and I have to believe that hurt the atmosphere as well. Starting 2014 with a lackluster win against Navy and a bad loss to Va Tech soured expectations and the stadium's energy for pretty much the entire season.
I also think that this fanbase has felt extremely insecure about the program since Glendale 2007 and New Orleans 2008. We're starting to forget it now after the miracle this past season, but those two losses were hanging over the program for almost a decade. I really think they made many OSU fans question whether the school's accolades, prestige and accomplishments were truly merited, and I have to believe that helped lead to more subdued, unsure and cynical crowds at Ohio Stadium.
But the program looks poised to dominate and the fans have rediscovered their bravado. And with a strong MSU, a Harbaugh-led Michigan and Bob Stoops' Sooners coming to the Shoe in the next few years I think we will see much better crowds.