Why be miserable and moaning when there's another option to be smiley, happy and friendly?
Because everyone is different and some people aren't bubbly happy extroverts?
We have permanently happy people, quiet ones who keep their heads down, ones who like to moan a bit, people who can't sit still and are up and down all day.
Everyone contributes to the team. Even the moaners- they are often justified and they are the ones who will raise issues with management while the smiley people pretend all is OK. The getting up and down ones can fetch tea and do printer runs for the ones who don't get our their chairs, the happy social people can organise leaving do's....
It would be boring if everyone was the same.