They're easier to fly because they have software providing artificial stability. If you had to control each rotor individually it would be virtually impossible. There's no reason in principle why a helicopter couldn't have similarly straightforward controls.
Why not provide a joystick for translation motion, rudder pedals for rotation, and a lever for ascending and descending? Allow the human to provide simple inputs, like: tilt the stick forward to go forward. No other inputs required. Aircraft will remain at the same altitude while it tilts forward and gains airspeed.
The computer consumes all of these controls, understands what the human wants to do, and then makes the necessary low-level adjustments. I suppose one obstacle to this plan is that the helicopter would need to be entirely fly-by-wire, and there would be no fallback to manual control. This would likely make the helicopter more complex and expensive.
http://www.helicoptermaintenancemagazine.com/article/underst...
At the Hiller Museum in San Mateo one of the docents was talking about how helicopters seem so great but they are so hard to fly with the pilot managing rotor pitch, rotor speed, and countering torque with the tail rotor. A typical quad/hexa/octo copter type vehicle is much easier to fly. (as is a gyrocopter but it cannot really take off vertically)