I'm having a hard time understanding your statement. Both functions are done by the same head so if there is any wear from either function both functions are impaired. An entirely worse scenario than using two separate bits.

This combo-bit is essentially an exceptionally dull 4 fluted drill bit. Any time possibly saved in not swapping bits is lost to the slower drilling speed due to the dullness. The fact that it only works with Phillips screw heads also slows things down due to the greater care needed to avoid stripping the screw head and the work required to remove a stripped screw head when it does occur.

It's not like people have not though about how to do this faster it is just that there are existing alternative solutions that are far superior. Amortizing swaps over multiple screws, using a second drill, having a quick change chuck, using self tapping screws and possibly others that I don't know about.