As a current student I figured I would give my two cents on why I think the tickets are tickets getting bought. I don't think it's because they are harder to sell in fact the online ones are much easier to sell. Instead of having to meet up in person or mail someone the ticket I can just email it to them or even take a screenshot of the ticket and text it to them. Plus the new tickets don't even say student ticket on them so if you enter in any random gate the usher don't know that you need to show a buckID much less care. Also the non-conference schedule doesn't really matter because students can buy a Big Ten only package. Also for students the hype around the Penn State game is just about the same as for ttun games so when you have Penn State, Michigan State, and Wisconsin on the home schedule that excuse doesn't work that well either.
I think the big reason is the tailgating I have several friends who bought tickets as freshman but don't anymore and instead wake up tailgate and then sleep during the game. Another issue is that as Ohio State becomes a more exclusive school the more of a certain type of student is attracted to it one that cares more about the average ACT score of the student body than the quality of the football or any other sports team. And the out of state scholarships that make Ohio State the cheapest Big Ten school even for out of state students mean I have meet other students that claim their favorite team is Penn State, Northwestern, or even ttun.