Why would my neighbors invite me to their engagement party but when I see them they don’t seem really interested in talking to me?

They’re both really busy resident physicians so I completely respect that they don’t have a lot of bandwidth. When we do talk they’re nice but we’re not extremely close. They invited me to their engagement party and I’m looking forward to going, but I’m also confused why I was invited if we’re not extremely close! I don't know the behavior kind of confuses me.

Why would my neighbors invite me to their engagement party but when I see them they don’t seem really interested in talking to me?
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