While shopping, people wear masks, talk (and breathe and cough) less, and are generally not packed into small spaces breathing a lot of the same air, so the risk is lower than at a house party or bar or dance club.

The same force that prevents covid from spreading while you are sitting down at a restaurant but can get you as you walk in and when you use the restroom

Mask wearing is well adhered too, and shop visitors stay only a short time, leaving less droplets in the air than maskless visitors to, say, a restaurant or bar.