A part of being a celebrity is to appear friendly to everyone, and cherry pick those they're going to extend time and sincerity towards.
Caring about others is the opposite of being in the zone, caring about others requires a wandering mind, because there is so much to care about. To even stop and think about who our friends are requires enough mental energy to pull us out of any focus.
Sometimes to care about people we have to clear our minds, and focus on our own stuff.
I want to be successful so I can be better towards others. Until then I'll keep a tight circle, so I don't strain myself out on social responsibility. I believe the ability to detach is separates celebrities from the rest of us.
That said it's probably not a good idea to be friends with a celebrity, but when they disappear it's hardly personal.