YOU'RE the ones attacking US you conniving filth! We're just defending ourselves from your incessant meddling! You're like flies! You BLUbloods wouldn't know what hard work means! The best offense is a strong defense. IT'S RED OR DEAD!
Oh really! Well this is a little something Valve has to say "The last Control point in many maps are mostly doomsday-devices, like great missiles, rockets and bombs. therefore, BLU tries to stop RED from making unbalance in the world." We are the ones stoping you from blowing the world up basically.
Those aren't OUR bombs, rockets, and missiles, sweetheart. We're just sent there to guard them from you. The administrator is both my boss and yours, and you know that. She just tells me to guard those things, so I do what I'm told. It's your capturing of the points that sets the things off. If RED wins, they stay undetonated.
Basically ,Blu is trying to take land from Red.team if you read the comics. And besides, Blu still has to defend their base from Red when it comes to Dustbowl. And don't forget, Theres still Payload race, Control points, Delivery and capture the Flag. So Blu still needs to defend after all that hard work.