Girl apologizes whenever she walks past me?

Hey everyone I have noticed these couple of girls that I know and whenever one of them enters my space or even just walks past me they say a quick "sorry". Like what are they sorry about? I might get if we were closer that I had to slant my body to get by, but no there is plenty of room and they apologize when they walk past me anyway?

Girl apologizes whenever she walks past me?
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