Why Isn’t Everyone Wearing a Mask in Grocery Stores?

So I'm confused, I thought everyone was supposed to wear masks in grocery stores and pharmacies to limit the spread of COVID-19 in Michigan. Am I wrong? Did I miss something about this?

Last week I walked into Rite Aid and totally forgot to put my mask on because I forgot it in my truck. The employee kindly asked me if I had one. I told her I forgot it in my truck but I'd run back out and grab it. I thanked her for reminding me because I literally wasn't thinking about it when I walked in. As I got back into the store, I looked around and noticed every person in there had a mask on (which was a good thing).

Over the weekend I made stops at Sam's Club and Kroger and while I wore a mask, there were so many people that were not. I don't mean one or two, there were a lot of people not wearing them. Now, I'm not judging here, I'm just wondering if this is just an option? Is it based on the store's policy?

Honestly, I don't care if you wear one or you don't, I just thought we were required to.