Again it comes down to basic principals. The better players make more money. A team that spends twice as much as another team (or most of the league) buys twice the talent. Talent translates into wins. Wins translate into popularity, marketing, and profits. The rich get richer. The poor get poorer. The rich buy more talent. The poor are forced to trade or let their talent walk.
People watch the NFL because of the any given sunday mentality. Parity. Your theory that economic disparity leads to competitive parity somehow is not only counter-intuitive and logically flawed, but has also been disproven by other leagues.