Not sure why you believe this.
If you aggregate soccer TV viewership (MLS, various Euro leagues, US National Team, etc), it is already one of the most watched sports in the US (easily top ten, probably top five).
Looking at revenue, MLS is just a piece of the pie. For example, MLS/US Soccer just signed a media deal running through 2022 netting $90M/yr... while the Premier League just signed a US broadcast rights deal running through 2022 for $177M/yr... while UEFA Champions league has a deal running through 2018 for $83M/yr... etc, etc. That's not including the FIFA World Cup or other periodic tournaments that don't have a "per year" figure. There's a lot of moving parts, each with their own media deal in the US.
Meanwhile, the "record-breaking" NHL deal signed in 2011 pays out $200M annually through 2021.
Not to get in the way of your denigration of the NHL, but the "record-breaking" deal you cite doesn't account for local deals. For example, the NJ Devils, who are not one of the leagues most popular teams, get $24 million per year from MSG. If you want to compare tv rights $, don't you think the total (local / national deals) is the only way to get an apples to apples comparison.
I think soccer is a great sport, but people are really letting their biases show on this one. For example, if it is so much more popular, why aren't there more youth players in the U.S. (or at least, more players registered with US Youth Soccer) than there were in the year 2000?
Stats from US Youth Soccer:
2000 - 3,020,442
2005 - 3,050,465
2007 - 3,123,698
2008 - 3,148,114
2009 - 3,094,868
2010 - 3,036,438
2011 - 3,025,551
2012 - 3,020,633
2013 - 2,804,711
2014 - 3,055,148