My buddy has had two family tickets since the 70s in the corner of the endzone, halfway up the bowl. In the past five seasons or so, those tickets have gone up from $65 to $110 face value. As we watched the Packers/Eagles game together from the Twin Cities (because neither of us could make a Thursday night game), he showed me that he lost about $5 off of face value selling his tickets. It was the same for the Broncos game that he couldn't make, losing money. Prices have gone up a lot, and face value doesn't include the personal seat license cost.
The number of "primetime" games also makes it harder for fans to go. Those tickets then get sold on the open market to anybody willing to pay.
I was a long-time college football season ticket holder. The coerced "donation" ticked me off, and the fact that I didn't want to sell my unused tickets on the open market. I always tried to sell or give my tickets away when I couldn't go, but then preferred that my seat stay empty versus sold to a fan of the other team. I eventually was losing too much money on the tickets and gave them up.
The ticket model and, to some extent the scheduling, for professional and college sports leads to these types of issues.