No mandatory play doesn't seem to be hurting travel-ball and the vast number of tournaments that are played that way.
Getting rid of MPR would cause kids to not want to be on the team and/or parents not letting them be on the team. Been there. Not pleasant.
It's about winning, but not to the point of exclusion.
And don't forget that the other team is under the same rules. You aren't losing advantage by having to play your subs because they have the same constraints.
It's no secret that the better kids, at least in our area, are flocking to travel-ball.
I'm not sure if other organizations, (Pony, Cal Ripken, ASA, etc.) have MPR in All Stars.
It would be interesting to know.
To be sure, smart coaches play their kids no matter what, and travel-ball teams better play their kids as well, or risk losing players.
But the whole LL MPR requirements in All Stars is not the answer to declining participation.
It's another band-aid fix to a perceived problem.
The constraints are only the same if each team has the same number of players.