Salary Caps by sport

The salary cap for each sport has a pretty direct correlation between how much yearly revenue the sport brings in and the salary cap for each team. And with the numbers provide below you can see the correlation for yourself.

League			Salary Cap					Yearly Revenue
NHL			$59.9 Million					$2.9 Billion
NBA			$58.004 Million					$3.8 Billion
MLB			$178 Million					$7 Billion
NFL			$120 Million					$9 Billion

Sports such as the NFL and MLB which have huge yearly revenues have a much higher Salary cap than sports like the NBA and NHL. Also the MLB and NFL have many more players per team than the NBA and NHL. The NFL averages around 60 active players on the starting roster, while the NBA only has around 15 active players.