I watched a little before the Elite Eight games on Easter Sunday. It was okay, but lacking because there are no names, promotion, connection to fanbases, or emotion. For as popular as the NFL is, one cannot simply yell, "football!!" and expect people to come running.
The NFL is too big, offers too much money, and will no longer buy into a farm system (i.e. World League). Compared to baseball, where players enter their prime at about 27 years old, a football player's prime is around 24. There is no reason to season a given veteran lineman, when a young'un has equivalent skills and higher ceiling. Further, The NFL schedule is year round. Players don't work offseason jobs and use training camp to get into shape anymore and anyone decent is signed to a futures contract, preventing them from moonlighting in another league. If anyone is going to get hurt on the NFL's dime, it best be while NFL'ing. At the end of the day, expanded practice squad size and eligibility, along with an estimated 200 willing educational institutions already set up to provide equivalent services at virtually no cost to The Shield itself renders a structured farm system moot. The cost/benefit is not there for the rare late bloomer and I don't believe for a second that they aren't aware of all of that.
The USFL of the 80s worked opposite the NFL, because they could offer equivalent or better salaries to top prospects coming out of college. Even then, for all the "success" the USFL supposedly experienced, teams were still folding and emerging on a regular basis. Then [someone] had to challenge The Shield, and kill the golden goose completely. Not to mention, the effects of concussions and other injuries are far better known, so that no one with half of a brain over age 25 is willing to sacrifice it for comparable chicken feed or risk forfeiting life insurance proceeds.