Do owners have to field a team ?

The owners all have invested with the NFL for franchises to represent various cities in the league.  The cities in turn have invested millions for staudiums, upraded all roads and highways leading to the stadium and provided a loyal fan base for the owners.  Aren’t the owners responsible to field a team?  Couldn’t (or shouldn’t) they lose their franchise if they don’t field a team?

Just a question, give your opinion.