One reason given is that the job of shop-assisting is not highly regarded in Poland.
You might think of them as being beneath you, other people do not.
Those performing such jobs rarely are helpful to custoemrs,
I'd entirely disagree with that, but then I always treat shop staff as being my equals and am always polite to them. If you treat them as underlings and are rude to them, it's no surprise that they are rarely helpful to you.