I understand your frustration, but this is basically how it works. There are certain medals that encourage prolonging the game and farming the enemy team. They are:
75k damage
300k damage
10 kills
25 kills
1k defender points
3k defender points
Of these, the defender ones encourage the most heinous behavior. In huttball, you get them by killing the ball carrier. What's the easiest way to do this? Group up and wait for some fool from the enemy team to go on the offensive (there are always one or two heroes) and toss them the ball. You then quickly kill them and wait for the next victim. It's pretty funny and it's efficient.
Also, 50% of the time the stupid daily/weekly quest won't update when you win so there is no point to rushing victory.