Mask purpose?

Order my chicken on the fly thru then drove to the next window to pay. She asked i put on a mask while I'm in my car. I look for the mask I couldn't find it. So I took my sweater and wrapped it around my mouth. She still refused me to pay saying it's not a mask. Ended up leaving. So my question to Chicken Licken is, what's the purpose of a mask? Isn't it to cover your face? If I'm in my car and I cover my face with sweater it still not enough?