Two things:
1- soccer is one of the most accessible sports in the world
2- Youth recreationally soccer is big in the US
but Professional Soccer is still much more of a niche than the NHL. It is seen largely in the US as a game played by kids. Professional soccer is boring to most the US. The US because of it's population is able to compete in most sports, and US men's soccer is one of the laughing stocks of the world.
Since there aren't nearly as many professional women's league's the US ladies do much much better than the US men in both hockey and soccer.
Look at the revenues. The MLS is not passing the NHL anytime soon. the NHL's revenue is 5x that of the MLS
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List of professional sports leagues by revenue - Wikipedia