Personally, I look at the use of decoys somewhat akin to the use of "rattling" deer antlers, both being something that is often, maybe more often, as much liability as asset. 

Particularly in the big scheme of things, the potential benefits of either have been very over-stated, while the liabilities rarely mentioned, I supposed, because money is made in the selling of both decoys & rattling horns?

Sometimes, deer decoys also work great.

So why don't more deer hunters use deer decoys?

One reason is you can do more spooking of deer than attracting of deer via using those decoys.

Never mind the pain in the butt of using ANY decoys.