[kocsenc]

I think its mostly the fact that technology caught up and became cheap enough. Battery technology, motor technology (brushless), electronics (ESC's which control the motors, and the onboard boards with gyros and accelerometers) and many other things.

I'd attribute it the most to battery technology. As part of the hobby myself, Ni-Cad batteries were the go-to's. But they were crappy. Li-Pos have existed before, but the thing about multi-rotors and flying in general is it doesn't need a high capacity, but a high output rate, which we can get now.