I think it's more a case of what is ingrained into everyone.
you score a try and then you take a conversion.
In the heat of battle, it's very rare for someone to go completely against the norm.
And if they do, half the time they'll make crazy, poor decisions.
If it became a "thing" that quick drop goals were being taken after trys with very little chance of success, I suspect that we'd see a law change to ban it
(even though it achieves more in field ball time, which is what the powers that be are after)