To those who fly in UK, we fly inverted all the time compared to those in Australia - and visa versa.
The question is worthy of technical debate but as often stressed - why would anyone wish to build a helicopter (mega, mega bucks) with an ability that would not be rational.
It's almost similar to asking why can't all boats be fitted with wheels so that they could operate on land. Or why can't all airplanes land on water and submerge.