There is no obligation to say hi. People are different and it's fine. If one of the regulars is just always reading or something, no one else cares. The closes

There is no obligation to say hi. People are different and it's fine. If one of the regulars is just always reading or something, no one else cares. The closest thing to a problem is you'd have to be ok with someone else initiating and approaching you once in a while, but probably only once if you don't encourage it.