These rising salaries are tied to the ever increasing value of broadcast deals. It used to be a battle between the networks - CBS vs FOX. Then you add DirecTV to the mix. Then ESPN, then Amazon. Each step adds more money into the pot. And for the broadcast networks, their ratings have been declining for years, except...live sports. Especially football. Sunday Night Football is usually the most watched broadcast show ever week it's on.
It's not $50 parking or $18 beers or PSL's or other ways the NFL is trying to exclude low income fans, it's the tv money.