Why does he sit next to me and not across from me?

I go to lunch with the same co-worker everyday, sometimes just the two of us sometimes in a group. Whenever its just us, he always sits next to me and never across from me at the table which feels very unnatural to me. Why would he do this? Am I the "odd" one for expecting him to sit across from me? To me I feel like its easier to talk to someone your facing instead of having to turn to see them.
Why does he sit next to me and not across from me?
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