Easy...easy...let's not start beating up on the Pirates!
Besides, a fleet in planetary or system orbit has a chance to engage the Corsair or Volsair fleet. I know....I've had several fleets wiped out on raiding runs. They aren't the most durable boats in the game, after all. Rift Corsairs and Rift Volsairs have made it easier, but you still have to run the final gauntlet through system space.