Why won't people move out of the line of traffic in stores?

Question

and then give you dirty looks as if YOU are in THEIR way?

Answer 1

Maybe they still think their driving. Imagine if they were in a car?! :)  

Answer 2

Because they are not paying attention and become defensive and embarrassed when caught out.

Answer 3

...because they're ignorant, and care about nobody but themselves.

Answer 4

Hereditary territorial claiming practices. By putting themselves in your way they make you choose to invade their "space" or avoid them. If you avoid them then you legitimize their claim to that "space". Same thing happens in parking lots. Notice that when someone gets in a car, they will actually take longer to vacate their parking space if they know someone else is waiting for it.