Between the 1985 and 1986 baseball seasons, Major League Baseball decided to move the non-waiver trade deadline from its longtime date of June 15th to July 31st. It was a big change, but it was deemed necessary, as the middle of June was too soon to determine whether or not a team was a playoff contender or not. After the change, teams that were relatively far removed from a chance for a playoff spot could shop their best components to contending teams and receive some prospects in return. The system worked fairly well for awhile when there were only four playoff spots to be obtained.
Unfortunately, flaws in the system began to emerge when more playoff spots were created. This problem would only emerge in some years though. There were still deadline deals, but teams were more reticent surrender their season with the addition of the Wild Card. Now that there are two more playoff spots, it is even more unlikely that teams will give up on their season, unless they really want to irritate their fanbase. As of right now, only eight MLB teams are further than seven games out of a playoff spot. The vast majority of teams can still rightfully consider themselves "in the hunt." There are only so many trade partner combinations possible between the contenders and non-contenders.
It is for this obvious reason that the trade deadline can no longer remain on July 31st. It is simply too soon for teams to make a proper analysis of how their seasons are proceeding. Another 15 days of the season could help though. Extending the trade deadline to August 15th will not necessarily always sort the contenders from the non-contenders, but it would give more time. Deciding whether or not your team is capable of making up a big deficit is a little easier when there are only about 45 games left instead of 60.
Last year's Pittsburgh Pirates were so clearly still in the race that they were buyers at the trade deadline for the first time in years. Unfortunately, the move was for naught, as by August 15th, they had descended into a tailspin and were crashing to another 90-loss season. If they had a later trade deadline to work with, perhaps they could have dealt a player from their team for prospects. If the Mets can tread water until the deadline, they might be buyers as well. However, if they fall out of the race between July 31st and August 15th, the city will be abuzz about why GM Sandy Alderson didn't trade Johan Santana for prospects. It might not even be so bad to extend the deadline to August 31st, too. Ten playoff teams is a third of the league, so plenty of teams have a chance to make it, even if they're not too close to a spot in mid-August.
Give the teams more time for self-assessment. Bud Selig wanted more playoff teams, and he got them. Now, though, he must live with the consequences--an extremely inactive trade deadline.