I take it that you have never seen a sack of feed infested with grain mites and or other 'very small' bugs. By your logic there would be no lice nor mites in the coop either. They are too small to be picked out and or eaten, except by accident. Grain bugs are small, they eat grain, leaving behind dust and poo, depending on how long you wish to leave the infected bag around, they can and will consume the entire continents of the sack, and then move to any other feed they can get to. So feeding it to your chickens turns mites loose into your coop, where they will find grain/feed to eat and happily live there forever after. Does a sack of hollow grain hulls and mite poo sound like something you would wish to feed your livestock? Does your flock thrive on mite poo?
Yes, the birds will eat it, that is not the point. It is the ignorance of turning loose a bunch of grain/feed eating mites on your own coop.
RJ