I don't think you can just blanketly say playing in Europe is more valuable compared to MLS. Outside of the 2-3 top-table superpowers, teams in Belgium and the Netherlands are not much better than MLS teams. Even the top leagues in France and Italy fall off hard in quality towards the bottom of the table. Sure if a guy can make it in the Premier League or Bundesliga that is a much higher level of competition week in and week out and they should go for it but that's not the situation a lot of these guys are in. They are floating around to teams outside of the top leagues and still just sitting on the bench. Even the players on the top teams in places like Italy spend half their season playing on a super team against some crap team at the bottom of the table.
In MLS they would get consistent time in a parity-driven league where most matches are close and competitive. Many of the teams in MLS have former European coaching staffs so it's not like some secret coaching methods are happening in Europe that don't exist in MLS. Going to Europe is wildly over-glamorized by USMNT fans who act like every player is going over to start for Real Madrid when in reality a lot of them are sitting on benches in leagues that are not any better than MLS.