A lot of people are focusing on the quantity of seats as opposed to the quality of seats.
Why did *two* NFL teams leave LA? It wasn't because they didn't have enough seats. In fact, they had plenty. The Raiders were in the LA Coliseum with 90,000-plus seats. It was the fact that they didn't have stadiums with enough *luxury* seats.
Same thing with the NBA leaving Seattle. Key Arena is a perfectly serviceable 17,000-seat basketball arena on paper... except that it doesn't have enough luxury seats which makes it untenable in the eyes of NBA owners (whether that's fair or not).
This is also where college sports stadium expansions and renovations are heading. That's why Louisville has been able to show such a massive revenue increase with its new basketball arena and recent renovation of Papa John's Stadium - it's the sale of all of those luxury suites more than anything. That was the focus of TCU's latest stadium renovation, too - overall capacity went up by less than 700 seats, but the new suite revenue is going to generate exponentially more ticket money than what they were getting previously (even beyond their new Big 12 conference revenue). It's also what Tulane and Houston are doing with their new stadiums (that are "right-sized" for on-campus games). Rutgers installed over 1000 new premium seats as part of its football stadium expansion.
So, Cincinnati isn't adding in 5000 seats for the sake of increasing capacity by 5000. These aren't going to be bleacher seats. Instead, most of them are going to be high end suites and box seats that are going to require large donations and leasing fees on top of the price of game day tickets. 1 luxury seat sold could easily be worth the revenue of 10 regular seats sold, so the idea is that those 5000 extra seats are going to be high impact revenue generators (not just to get the capacity number higher, which is tangentially helpful but not the real purpose).
As a result, the Rent likely doesn't need to add tens of thousands of "normal" seats, but adding even just a couple of thousand premium seats can make a big difference to the athletic department's revenue line (which in turn gets you a further look from power conferences in the way that Louisville's revenue jumped out at them). Sheer attendance is nice for press releases, but there is increasingly more focus on getting more out of a smaller and more moneyed pool of supporters via luxury suites as opposed to attempting to pack as many people into a stadium as possible.
