It is not a requirement, it is not a tax. If you find it objectionable don't do it. By your logic we should all resent any entrepreneur or in this instance any entertainer for making money.
http://bleacherreport.com/articles/2527998-why-are-nfl-teams-no-longer-traveling-for-training-camp
Only twelve teams travel to camp, which means twenty do not including both of last year's Super Bowl teams. I also believe that the Bills training camp portion at SJF is a week shorter. And I did listen.