Sometimes I think manufacturers are stuck in very old ways of solving problems. Gearboxes being one of them.
It would obviously be fully feasible to design a rotor system without a metal-against-metal-soaked-in-oil grinding gearbox - either with belts or by having a bigger diameter turbine stage and direct drive the rotor.
Maybe manufacturers of big helicopters should take a look at how far the RC heli's rotor systems have improved over the years.