Why do people believe this?

When I see people asking how to write characters from different cultures and incorporate cultural elements or cultural stories, I too often see this stated as if it should be fact, and too often no one bothers to question this "fact" or why we believe it or why it could come from a harmful perspective.

Sure, no one may "own" culture in the Western legal sense of "property", but we are still faced with language that only serves the privileged appropriator and leaves no recourse of objection for the appropriated.

I often talk about "my culture" and obviously the people asking these questions recognize they are talking about a culture not their own. So how can they then conclude that no one owns it?

How can we change this pervasive perspective?