Why do most MLS games on TV overun the allotted time?

When ESPN , FoxSports televise 'live' games from Europe on North American TV, the games always finish within the 2 hour time frame allotted (unless it's a cup game with extra-time or penalties possible). However, when they broadcast 'live' MLS games, none of them ever finish in the two hours allowed, meaning the next scheduled programme never starts on time.....if this is down to the ever-increasing number of commercials....why don't the networks simply add an extra 15 or 30 minutes to the time?