Why did Gladwell make such egregious mistakes and resort to lazy, analysis? Why did most readers lazily accept such explanations without asking relevant questions? Why do journalists immediately jump to cultural explanations in lots of cases without having a strong understanding of the facts, the details and/or actual knowledge of the cultures that they are holding accountable?
Because culturalism makes us feel informed and superior. It allows us to form a sophisticated-sounding opinion that confirms your own cultural superiority without knowing anything. It allows us to quickly come to a wrong conclusion in a lot of different contexts - it's difficult to get to know a specific person, but it's easy to recall a cultural stereotype. We want to feel like we know what's going on, even when we have no idea. Culturalism gives us that feeling. It's knowledge saccharin.
This comes up a lot in technological contexts. for instance, with just programming languages and platforms, we see these (or some politely worded versions thereof) all the time: .NET developers are copy-pasting Microsoft drones who can't solve difficult problems without wizards holding hands, Lisp programmers are non-bathing egotists who can't work with others, Java programmers are cargo-cultists who prefer verbose incantations full of acronym soups and unnecessary hiearchies of meaningless classes to clear code, Perl/Ruby/Javascript programmers can only write short scripts, not maintainable, performant or critical applications.
The lesson here is clear - distinguish between actual knowledge of the world and poor, phony substitutes that merely give us the feeling of knowing. It'll make us better at what we do and incidentally also lead to a better society.