Why would Male coworker ignore me?

A male coworker seems to converse with both girls and guys in my office, but he just ignores me. When we do converse about a project he is to the point, but otherwise he avoids me and doesn’t put in much effort into a conversation. Same if we go to a conference, he’ll barely make any effort until usually we go after work drinks and he’ll sit near me.

I am well liked and usually get on with both males and females pretty easy, it’s just a bit weird to be ignored day in day out, when I don’t know why. It’s not like we have fallen out or anything.

Why would Male coworker ignore me?
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