[mac01021]

A large fraction of people in the "developed" world (perhaps a majority?) work as something like a cashier, for an employer they don't really care about. And they are all aware that most other people they meet are working similar jobs. So they don't ask, because they know they'll probably get a reply like "I stock shelves in a department store", which isn't going to lead anywhere interesting.

Because of this, if someone does ask them what they do, they can be pretty sure right away that that person does something "better" than what they do, and (wrongly or rightly) it can make the situation uncomfortable for them.

Obviously the extent to which this is relevant depends on the demographic of the group in which you're socializing at a particular moment.