Not a helicopter, nor an expert in them, but modern electrical engines are significantly more efficient than traditional ICE motors. Also, the scalability of existing small-form quadcopters (etc) means it's much easier for companies to start from the ground up with that sort of tech, rather than developing a complicated rotor/contra rotor set up.

Basically, it would have been very difficult to go the contemporary route in decades gone by, whilst it doesn't quite make as much sense for the usage scenarios to go the traditional route.