I don't know squat about design, but I suspect that a bolt gun trigger ain't got a light "hammer fall". As such in a drop in unit, I still think there would be a way to get one set up really good with enough weight to fire the primers every time.
I think.
But I'm so used to 2 stage, and I can't at all understand why anyone could not get used to them I just don't get it..
My buddy says same... his lower is going to have a crappy 5 pound polished GI trigger yanked in a week and a varmint RRA slapped in and I'm going to tell him tough, get used to it for a year, then we can take it back out again if it still bothers you...
Things are SO easy to shoot and get used to....