I freed frozen/thawed and most of the time my corns won't constrict. Sometimes, if they're feeling super aggressive, they might throw ah coil over. It also seems to depend upon how startled they are by the food. If I have to lead them to the prey, they just eat it. If I drop it in, and they strike at it, then maybe a coil comes out.
It isn't just corns either. My ball python will usually curl her neck up a bit, but not the full on multiple coils like I know she is capable of. I've even seen her just eat the prey item without ever constricting.
I'm with bitsy in thinking its an energy conservation strategy. Do you shoot your steak to make sure its dead? Probably not, and you wouldn't last long in a steakhouse if you did. Once the snake realizes the prey item isn't alive, why waste the energy?