Major League Soccer is unlike any other league in major American sports. Basketball and baseball and football are insular. There are very few leagues throughout the world. There is almost no interaction between those leagues. The sporting industry works in and of itself.
But football is not like that. The American league is not the elite league in the world, transfers can take place between leagues, this being the primary way of acquiring players, and the Americanisms of other U.S. sports do not apply in the same way.
There are squad rules that every team must abide by, for instance.