Probably because they find it uncomfortable to be pressed and the net result is a less productive relationship.
But is it productive to cooperate with someone who will never admit lack of information?
If they cannot take a step towards another culture, why should I?
If they are working for a western company, they should adjust their behaviour, not the company. Just imagine working for an Indian company (or manager), and expecting them to tolerate your individualist behaviour and audacious questions. You would be punished immediately.
If it's a peer-to-peer relationship, all the more reason to be firm. If you don't speak up you will never be respected. And don't think that just because you keep quiet the shitty types of people won't stab you in your back at their first opportunity (ask me how I know).