> Wouldn't the same apply to mask wearing?

No, for a ton of reasons. Off the top of my head:

(1) Masks are more effective at preventing transmission than reception.

(2) Different individuals have different levels of concern, which might lead one to choose a mask and another to choose not to wear one.

(3) Different individuals face different levels of risk. The person who is immunocompromised may wear a mask even when it would make no sense for other people.

(4) The customer may encounter 2-3 service employees in a day; the service employee may encounter hundreds of customers in the same time.

And that's without even getting into political issues (in the US, where mask-wearing has become politicized).