Because complex aircraft tend to do a lot of the work for you. Also, helicopters tend to demand more of your brain cycles to actually fly than fixed wing aircraft.
The weapon systems on the Ka-50 are actually simple to understand and operate, but the aircraft is more difficult to handle overall - navigation systems, datalink systems, etc are less automated. Proximity to the ground demans your constant attention, and the lack of a radar warning receiver means that you either don't go where there are fighters, or you have to be insanely paranoid.
When you say simpler aircraft but harder to fly whys that? And the same for combat? Are the systems more complex to learn and operate?