The trouble with alternatives is that the alternatives don't mean anything. The NFL has The Super Bowl. You can't reinvent that without time. And the best players are already in the NFL, so any other football product will be inferior.
The alternatives play in smaller markets where there is less money and it becomes a self-fulfilling prophecy of doom. What is interesting is the MLS has managed to see good to substantial sized and dedicated markets in Portland, Atlanta, Cincinnati, and Seattle. Even Orlando. And this is for third rate soccer, but it is the best domestically we have
Alternative football just doesn't carry any importance or legacy and it is second rate. A small portion of people are desperate for an alternative, but that group of people just isn't sizable enough to warrant the investment of hundreds of millions of dollars to make a league work, not nationally.