Why do people walk so close to me on the sidewalk?

I moved to a city, and I've been walking around a lot. When I'm walking toward someone, I'll of course try to move to one side. But occasionally, people will walk really close to me when there's the whole sidewalk. This one girl, I moved to the left, then she did, so I moved all the way to the right, and she followed, so when we passed by, I had maybe a few inches to move. Like why?

Why do people walk so close to me on the sidewalk?
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