Why do some (married) men who used to be friendly with me treat me coldly?

I never had any deeper interest in any of them but for some reason they went from friendly and polite to strictly professional and sometimes borderline rude. Now they go out of their way to be distant with me and show me that they are not interested in a friendship (no smiling, no small talk, looking to the side when greeting me) while being super warm and friendly with everybody else. Why do they behave like this? I never flirted with them and I rarely approach them and I was always polite

Why do some (married) men who used to be friendly with me treat me coldly?
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