The only way to get people to wear masks out in public / stores is for the stores to mandate it for entry. Without that mandate, half the people are going to go without masks (at least from what I've seen the last week or so).
You are right, but I think a lot of local stores are probably afraid of pissing off local customers. It's likely going to take an order from the Governor to get people to wear then in large enough numbers and to get people to continue wearing them.