Even assuming you don't mean culture as a proxy for race or religion (which are obviously related but not the same as culture), times being what they are when you hear "culture" from a stranger you don't usually think "oh interesting, an anthropologist!". Instead it's usually time to buckle up for a broad generalization about a very large group of people the speaker is no more familiar with than anyone else.

Because that's objective reality. Cultures do have statistically common behaviors/traditions/norms, some "good", some "bad" - that is literally a fundamental part of the very definition of culture. Acknowledging this obvious fact in a reasonable conversation is no more wrong than saying it's still not ok to drink and drive despite the fact that most impaired drivers do not cause any harm.

Mischaracterizing the simple acknowledgement of patterns of behavior as a claim that all members of a group always act that way, and no improvement is possible because the culture is fundamentally flawed, is incredibly disingenuous. Anyone who makes this claim should be ashamed of themselves, as it is attitudes like this that contribute to perpetuating disunity between cultures who will always be distinct. Cultural uniqueness is usually a good thing (and should be preserved), but not always.