Do they just not having small talk with you or in general they dislike small talk? I can’t imagine not acknowledging a colleague in public.

I don’t think professionalism is an issue here. Are these people never do small talk with others either? these particular people just have no interest in talking to you? I understand it hurts

Another thing is I am very social and talk to anyone, I can talk to a wall but I dislike small talks immensely. If you ask me if I am reading any good books currently, that’s a valid question and I’ll have a good response to it plus a follow up because if I don’t currently read anything good perhaps you have a suggestion re book to read. That’s a conversation. If you ask me if I am having a good day, it’s a small talk. I have nothing to respond but say yes. What am I going to say to this.

Some of it is cultural. In many cultures small talk is not common. We either say something in substance or we shut up. “How are you and if you had a good day” is nothing that requires any particular response besides “yes”. You might solicit better conversation if you ask what they actually did or if they saw/visited/made something while on break. Or share what you did or saw