reely, one reason may be the potential for ground resonance. (Model dependent). The other is that control rigging adjustments, particularly seasonal adjustments for autorotational NR, might run crosswise with a sort of "negative pitch" default blade pitch on the head that you are proposing.
I'd need to do a bit more asking around, but I also think that a negative pitch provision like that might unload the head and lead to some undesirable blade performance ... a bit of guess there, some of our aerodymanically bright folks can probably expand on that.
As to the ground resonance:
Some decades ago, we were doing a post maintenance check flight. Bird had a fully articulated head, and wheels not skids. Helo was on the ground, flat pitch (collective on the bottom). My boss and I were observing the operation, and his eyes got big. He motioned frantically and gave the cut signal. Engines shut down. He told me: "Oleo struts compressed, shoud not be compressed at flat pitch. We have a flight control rigging problem." He made reference to a bird that had gotten into ground resonance due to a crap rigging of this sort some years prior.
He was right. Rigging problem. It had to be corrected before we were going to try and put that bird into the air.
Not sure how viable your suggestion is.
@ sycamore: do Wasp or Lynx run into ground resonance in that mode very often?
