Why Are Some Macaroons Not Gluten Free?
Why Do Some Macaroons Have Flour?
Sometimes manufacturers will put flour in their macaroons to take up weight (that is, to make them bigger using cheaper ingredients like flour instead of coconut) and to help bind the macaroon together and make it easier to process. Most commercially manufactured macaroons are processed through a dropper machine that deposits the individual macaroons on a conveyor belt or a baking sheet. In order for the macaroon batter to flow through the machine most efficiently, the batter should be uniform and consistent.
Coconut, whether a manufacturer uses "macaroon shred" (a very finely shredded coconut), "flake coconut" (a more coarsely shredded coconut), or any other cut of coconut, has a particle size that is many many times larger than flour particles. Therefore, the more flour one uses in their recipe to replace coconut, the smoother the resulting batter will be, and the easier it will be to portion out that batter during the baking process.
What About Coconut Cookies?
If you want to make coconut cookies, a great way would be to add flour and drop the amount of coconut. But then isn't that just what a macaroon is?