The companies do regulate it. The NHL recently locked out it's players for an entire year. The NFL has a salary cap too, and the NBA has a soft salary cap. The players make big business for the owners, who in turn reward the players by providing them great salaries as well, and good for them. Consumers have determined that these athletes are worth the millions of dollars per year that they get.
Look at a league like the professional Lacrosse leagues, the maximum salary in those leagues is like $25,000 per year. Why? Because it isn't a big business and those owners don't make the money NFL owners do. In fact, it's common for 1 or 2 teams in a league like this to relocate every year because they aren't profitable in that market.