forgo daily

I understand being grateful when someone holds open a door for you. I feel it’s proper to thank them for the kind act. But here’s something that makes a bit less sense. I was walking in a hallway and came up to a rather narrow doorway. I saw a group coming from the other direction, and I feared the doorway wasn’t wide enough for two-way simultaneous traffic, so I decided to step aside and let them through first. Well, each of them thanked me as they went through, which struck me as odd. Why am I being thanked? I suppose I understand. It makes a little sense, but not much.