Yes, soccer is the #1 sport played by youth in the US and has been for about 10 years now. But a lot of those kids stop watching soccer when they grow up. Out of many of my friends that I played with when I was a kid, very little are still soccer fans. It isnt the "cool" thing to do, so they stop.
The MLS doesnt need to reform, it is progressing nicely and keeps getting better and better. They are expanding next season and attendance keeps increasing. Sports leagues dont boom overnight. It took the NFL several years to even become popular and not it is a monster.