Why don't say hello?

I have two guys co-workers at work. They're buddies of each other. Peter, who's been working there for a while and John, who Peter brought in two months ago. My office is a little further in from the corridor so it would take about four steps for someone to see me and say hello. But these two boys never do that, neither in the morning nor in the afternoon when they leave work. They only say hello to me when they see me in the corridor. Even though we are direct co-workers and all my other colleagues come to the door every day. Why do you think this is and should I tell them about it? It would be a bit embarrassing if I did. But it is also very unusual for me.

Why don't say hello?
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