Because the other side is likely "hot" at lethal voltage, and
nobody wants to be sued.
Not all IGBT driver ICs (in fact very few I see) are galvanically
isolated. But there should be some isolation, somewhere
between the user and the big hurt.
Short circuit and overvoltage protection are meant to make
the assembly survivable against momentary, credible faults
so that the unit will not be returned in warranty, not catch
fire, those kind of little things. Power line surges and
mop-in-the-drive-belt events are just part of industrial life,
and toughness is often a flowed-down requirement.