Most of them have already been mentioned, but I'll summarize things.
1) Team health on the defense. We had a large number of injured players coming into this game, especially on the defensive line. While some folks claimed that Howard Cross was about 85%, that was being overly generous. He was more like at about 2/3rd strength, but still played his heart out.
Rylie Mills, Jordan Bothelo, Boubacar Traore, etc., were all out, and Gabe Rubio wasn't at full strength either. I love Donovan Hinish for his "never say die" attitude, and his hard work, but he's an undersized 3 technique tackle who was filling in at the nose tackle position all too often.
While our guys were holding their own against that excellent tOSU offense, there was no depth behind them to step in for that championship game. You won't be able to hang with the best offense in the nation for a whole game if you don't have a lot of a quality depth to sub in.
2) Team health on the offense. Jeremiyah Love was hobbled, and the offensive line was a patchwork of able bodies. I give Coach Rudolph a ton of credit here. He was able to plug in different people into different spots along the offensive line as our guys were hobbled with injuries.
Also, after that first series, Riley Leonard looked gimpy after having run the ball so many times.
3) No consistent vertical passing game. This was a problem throughout the year, where Leonard was much more of a dink 'n dunk thrower, especially in the early part of the season. it wasn't until later on that his medium range throws became much better, which was why we were able to get as far as we did. In terms of receivers, we had decent, but not great, receivers.
Beaux Collins was decent, but didn't really put up WR1 type numbers. Jaden Greathouse really stepped up his game in the 2nd half of the season, and especially in the playoffs, to emerge as the WR1. Jordan Faison was decent as a WR2 / WR3. None of these guys were in the same category as tOSU's WR corps.
4) Most importantly, tOSU's talent level, depth, and team health were better than ours. Throughout a 16 game season, you need that depth to keep your guys rested and healthy.
The bottom line, though, is that even if we were healthy, tOSU would still have won that game 3 out of 4 times. They were simply that much better than everyone else in the playoffs.