As a hypothetical example, if you're designing a chair someone very large or small may have a different perspective than someone of average size.

So the causality in that case is different body results in different lived experience results in different perspective.

This isn't to say you can't learn these things in other ways (such as doing user studies, or previous experience) but it's not as easy to notice what you weren't paying attention to.

Another example might be targeting the Chinese market without being from China. It's not the only way, but think about the amount of travel and study required to get a similar perspective.

Meanwhile you have lots of people who already have the knowledge you're looking for.