I was recently in an accident where I hit another vehicle hard enough to break the transmission motor mount and now both of the brakes on the front end are locking up, why would it happen?

jack all 4 wheels up and check for brake equalization , making sure the rear brakes are working the same as the fronts. you could have a kink in the line to the rear brakes and your only stopping with the fronts. have somebody step on the brakes and hold it ,take a pry bar and try to turn the rear wheel, if it s turns check your fluid pressure to that wheel by opening the bleeder screw, tighten it while the brake pedal is all the way down & repeat if necissary.

And your vehicle was repaired by a profesional facility?? Have you brought this to thier attention? How long between the collision & the problem? Something overlooked during the repairs? Contact them for an inspection. Call your ins. co for a reinspect if you don't like the answer.