Seriously, this is the MLS's version of an all-star game?

Okay, so the MLS's all star game is everyone in the MLS against Manchester United FC. Really? Because Man Utd. is already playing a lot of teams in the MLS, but that's the World Football tour, not an all star game. Most all star games are one conference against another(ex: AFC vs NFC for the NFL, NL vs AL for the MLB, East vs West for the NBA, and I think NHL used to do East vs West before they did the draft thing.) So why does the MLS put everyone from both conferences against a European team?