You're ignoring that many of these MLS teams play in football stadiums which are substantially larger then baseball, basketball, and hockey stadiums. You're also ignoring how substantially more expensive MLB, NBA, and NHL tickets are then MLS. You're also ignoring how substantially higher television ratings are for MLB, NBA, and the NHL compared with MLS.
Soccer is a fine sport but MLS is no where near as popular as MLB, NBA, NFL, and NHL. Saying so is just ignorant.
Soccer stadiums are almost always smaller than their counterparts, and have more attendees.
Ich habe schon Pferde vor der Apotheke kotzen sehen.
2014 MLB Attendance - Major League Baseball - ESPN
2013-2014 NHL Attendance - National Hockey League - ESPN
2013-2014 NBA Attendance - National Basketball Association - ESPN
2013 NFL Football Attendance - National Football League - ESPN
The only sport that doesn't have insanely great attendance is baseball and that's mostly because it's just such a long season that it makes going to EVERY game too expensive for the average fan, especially when games are constantly on television. You're specifically cherry picking two historically awful MLB teams in the Mariners and Astros.
No matter how you slice it, it's just ignorance to say MLS is more popular than MLB, NBA, and NHL. Soccer is a fine sport but it's just not close. I have to know how horribly wrong you are on the subject, so I just don't see the point in all of these posts. I'm a huge hockey fan but recognize that the sport clearly lags behind the other three in terms of popularity in the United States. So what? It's still a great sport.