So are you saying that SOP if the TSA officer doesn't have/can't find/is too lazy to look for keys is to breach the zipper?
Nope, not SOP, but it's done. If the bag can't be properly inspected, it can't go on the plane.
Usually the lock would be cut off, though.
The proper course of action when a bag can't be opened (usually in cases of a non-TSA lock on a hard shell case, i.e., lock can't be cut off) is to have the airlines contact the passenger, who then needs to come to the checked baggage area to unlock the bag.
In most cases, when the zipper breaks, it's on an older bag that's seen a lot of wear and tear, and/or the bag is seriously overstuffed, and the zipper comes off the track while trying to close it. It does happen!