system
Given the following post, respond as if you're commenting on Reddit:
human
Why are quadcopters not used for full scale applications the way that regular helicopters have been for a long time?

It seems like quad copter drones are the all the rage, ultra stable flight machines for miniature use. Are they useful for applications that regular helicopters are currently used for? Why/why not?
gpt
If your are taking about one a human is piloting the big difference is the computer.

Helicopters and basic planes can be flown with manual controls.

A quadrocoper depends completely on a computer to balance the props.

Now high ends jets also depend on computers but often have three way redundancy and cost a lot of money.

The toys also fly using electric motors with variable speed, there are a few out now that use variable  pitch in the blades.

Electric motors probably would be too heavy including power.source at full size. Gas motors would probably work with variable pitch blades but be expensive.

Tl;Dr: safety, power to weight ratio, cost/ complexity.