Dragon Ball sucks. We all know it. Not because of the design of the event itself, per se, but because of the rewards associated with the activity.
Here's how your typical match of Dragon Ball goes. Sooner or later, usually fairly early on, one team will establish a dominant lead of say 100 points or so. Once the lead appears insurmountable, many of players who see they're on the losing team will just ditch the match. Of course the game will pull in new joins to fill the empty slots, but few of them will stick around once they see they've been added to a team that isn't going to win. This usually results in the losing team having a rotating roster the entire match and finishing a man down. I do this when I see I'm on the losing side, and I'm not even a little bit ashamed to admit it, nor do I blame any other player for doing the same. The fault is ANet's for designing the event the way they have. The rewards for the activity encourage unsportsmanlike conduct.
Wins and wins alone count towards the Dragon Ball Champion achievement, which gives you the Token of the Dragon Ball Champion, which allows you to purchase more Divine Lucky Envelopes per day. Unless a player just finds Dragon Ball to be an exceptionally fun way to pass the time (why?), I'm willing to bet that most people are playing a match to get that Token.
Fixing Dragon Ball would be simple, and the fix would not, and should not, involve punishing people who exit the match early. It should reward you simply for playing a match to completion, win or lose (and no, the daily Dragon Ball Participant achievement doesn't count). If you earned progress towards that Token and associated Divine Envelope just by completing a match, rather than exclusively winning, you'd see a LOT more players sticking around for an entire game, and being more easygoing about doing so. Double the amount of matches that it takes to reach it if you must, and go ahead and give Little Lucky Envelope rewards only to the winning team. But until players are rewarded for participation rather than exclusively winning, Dragon Ball will continue to suck.