@CW-BornConfuzzledLeftILoveYa
Why? They're rarely made well. Baked raisins (see Heather Jedrus) have sort of a vaguely-meaty texture while rolled oats are more or less flakes of cardboard, if you cook naively. Because of the textures, the rest of the cookie generally ends up more like a dense cake than a cookie, and becomes too sweet (yes, that's a thing, at least for me) to compensate for the dryness of the oats. And there's usually sort of a greasy feel to them that's less bad than out of place, something you'd expect from a peanut butter cookie.
That's not to say they're bad, just that they're hard to make well, and it often comes off like health food trying to resemble something you might actually want to eat.