The other part of the problem is how US sports use their minor league teams. That doesn't exist in soccer. Reserve squads play in reserve squad leagues, not in the lower divisions. Players are "loaned" out to lower division squads to gain experience, however once a player is loaned out, you are forbidden from pulling him back to your squad until his loan term is up, so you best 20-25 players are playing in the reserve team or at the top club, not in some minor league affiliate.
The only teams that could come up in baseball and hockey, are owned by top flight teams, so it would be a drastic change.
The NBA only just now has a D-League (development league) and there is no minor leagues for the NFL.
It would be a drastic change in how things work and there's no way the owners or the unions would support it.