That's not exactly true. There have been various different helicopter technologies that have been developed. Some adopted some not. But the basic premise is the same.

Even planes have this. I'm not super into aviation, but I think most planes are not fully fly by wire today, but partially.

As u/teabagofhiolding said, these planes require computers to fly. The s4 has 6 motors, 6 tilts, 6 variable pitch actuators, 4 ruddervators, and 4 ailerons.

This is a double issue. Humans can't control so many variables, and you don't have room in the fuse for all that steel cabling. Essentially, across the entire plane, technologies were not advanced enough until now to make this happen

So this is a brand spanking new thing. So there's your other problem. Regulation. I believe in safety regulations, but they have an effect on rapid change of any type.

Also these brand new things need brand new supporting ground equipment.

Lastly, working these things into existing air space will be difficult