For the record, I would want to stay around 47-48k. Also, Northwestern is smaller by a lot at 35k, though they are a notable exception.
As to why, that's just economics. Giving a product away for free devalues the product you sold (ie. season ticket holders and full-price customers). I considered buying season tickets last year and did the math, and it was comparable to buy single-game tickets to the UN by game. Because of the sales, I ended up saving over $100 by buying individual tickets over getting a season ticket in the Upper North. Same with several coworkers that sat next to me. If you want to incentivize somebody to not buy a full-price ticket, set the expectation that every game is gonna be on a fire sale at some point.
Judging by how quiet the crowd was in the Upper East when it was full of staffers against VT, I don't think giving away tickets necessarily meant more enthusiasm.
Attendance is rising, but in the recent high water marks in GT history, we were attracting around 41k from 1999-2001 (including pre-UN), 48-50k in the big games from 2008-09, and 47-52k in 2014. Moreover since 2008, CFB attendance is down across the board 10%. There is a macro trend of fans staying home that are affecting every team, even if we consider ourselves the exception. Unless we start making the CFP consistently, I don't see us beating those marks consistently.
Our goal should not be to make it so small that we can jack up the prices. That's an awful precedent and it goes against AD RA and Pres Cabrera's ethos of bringing new eyes to campus. But we also should not have a stadium so big that we need to give away 8-10k tickets as a top-12 team against a conference opponent!