Why do guys feel like they have to wait to open door for someone?

I was at least one staircase away, and one of my co-workers ( who I don't know super well) decided to wait for me, causing me to run towards him so I don't let him wait for me for too long. Why do some guys feel like they have to wait so long and open door for you?

Why do guys feel like they have to wait to open door for someone?
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