The sport of boxing is the prime example. It was hugely popular. People gathered around the radio, then TV to watch big matches. Then money came in and greed. It was on HBO. Then pay-per-view. Well, then it died. Suddenly. The product was mediocre and the asking price was stupid.
A little thing called the UFC started up and well, the rest is history.
Could the UFL be the NFL's UFC? We'll see........