The patient man with a modicum of mechanical savvy and some oilstones, can make a 2 stage trigger sweet enough to make angels sing.with joy. Why, since single stage are just as good for a light crisp pull?
3 reasons, safety, safety and lastly safety. You can drop it, you can thump the butt on a concrete floor, you can accidentally brush it when closing the bolt, you can pull the trigger with the safety on and then move the safety to fire and the rifle will not discharge, you can slam the bolt home as fast and hard as human muscle will permit...it ain't going to go off. There is a reason that liability conscious Savage came up the accu-trigger...it solved 2 issues, it gave customers a target grade trigger pull but it added a large margin of safety, almost lawyer proof. Smarter people than me have referred to a well tuned 2 stage as "the poor man's set trigger". When hunting in the company of my family, I use a 2 stage with a striker block safety in the form of a Win model 54.
