Why is Trade Secrets banned in EDH or Commander?
Commander/EDH is a community-moderated format. Its banned list is not managed by Wizards of the Coast or the DCI. Official announcements from the EDH Rules Committee an be found on mtgcommander.net.

In this case, the April 2013 banned list announcement explains (emphasis added):


  Trade Secrets is much like Limited Resources in that has some issues in a multiplayer environment. It isn't a problem when one player draws four cards and another draws eight. Trade Secrets is a problem when both players decide to draw 80 cards and effectively turn a four-player game into a two-player game. It just doesn't add enough to the format to justify the games that it single-handedly ruins.




Duel Commander, also known as "French" 1-on-1 EDH, has a separate rules committee and banned list. You can find their official postings on duelcommander.com. Trade Secrets isn't banned in Duel Commander, since it's not a problem outside multiplayer formats.