Sure, it's their job but some people simply appreciate being left alone and unsolicited offers just come off as pushy.

Your parent comment is right: it's culture shock. As a German I can't stand the idea of having to shop in American supermarkets. And it's likely no accident that WalMart failed to get a foot into the German market -- not just because of their blatant disregard for German labour laws (which are more worker-friendly than in the US).