Surely the bouncing betty doesn't explode the moment you step on it, otherwise it wouldn't "jump"?
It's still a detonation. Once you've triggered it the propulsion charge ignites. The mine shoots up and the primary charge detonates. It all happens very quickly. But the fact is, the moment a pressure plate is triggered, that mine is going to go off. There's no standing on it.
The only time pressure plates are used that function similar to this manner are anti tampering devices. Say you stack 3 AT mines ontop of eachother, the one on the bottom has the pressure switch pressed and if you remove the top mines it will detonate. The mine is already primed in this way though and the similarities end there.
Quite simply what it comes down to is that Mines are intended to create casualties. Not outright kill. Similarly, AT mines can't be destructive enough to erase a tank, so often times the vehicle is a mobility kill. You maximize casualties by having mines detonate as soon as they are triggered. If you allowed mines to be defused by some silly Hollywood notion of tension the number of casualties inflicted would be lessened.