I would say the way MLS has structured its league may also be harming the growth in popularity of the game. To keep from making the same mistake that the NASL did in the 1970s where the New York Cosmos with Pele dominated the league, MLS decided to limit the number of "designated players" on each club and place a somewhat hard salary cap on the payroll for each club.

As a result, if MLS wants any big name players on European clubs to play in the league, then clubs have to wait until the player is on the downhill or "washed up" by European standards. For example, David Beckham, Wayne Rooney, Steven Gerrad, and Zlatan Ibrahimovic didn't sign with a MLS club until their playing days in Europe were pretty much over. Oddly enough MLS has even classified several Americans as "designated players." Some examples include Michael Bradley, Jozy Altidore, Tim Howard, Alejandro Bedoya, Clint Dempsey, DaMarcus Beasley, Landon Donovan, Claudio Reyna, Freddy Adu, Sacha Kljestan, and Graham Zusi.

If MLS wants to grow, then at some point it will have to lift the salary cap and allow owners to spend money. The day MLS has arrived is the day a well known European player (maybe not a superstar) while still in his prime decides to sign with a MLS club instead of a European club. It probably doesn't help that MLS's 2 transfer windows are not in sync with the rest of the world.