It's clear the Braves do not want the blow back from preventing Acuna from doing this. Neither from the MLB nor from the locker room by pissing off your franchise player.
And this is all pretty overblown. I can assure you that tons of players around the league are not sitting around in a protective bubble in the off-season. Acuna isn't the only MLB latin star that goes home to play winter ball. I remember reading a few yeas ago about a Phillies player that did competitive MMA in the offseason. Victorino or Pence maybe? Can't remember. And in the NBA, players play pick up games ALL the time in the off-season.