Why screw drivers are shaped the way they are

Push the screwdriver into the screw or you will simply strip the head of the screw with much less effort.

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Any screw that requires that much torque will instantly strip when you try to apply it.

That's a shitty version in the picture though. The good ones have the hex-shapes on the actual shaft of the screwdriver so your applying the torque to the metal, not the resin. Also the relatively sharps edges can be painful.

Negative the pressure applied will crack the handle

I think it's actually so you can grip and turn it better. A round screwdriver would just slip in your grip.