Humans overwhelming group themselves with groups that provide themselves with the best value prop. When the individuals circumstances change, which causes the value prop of the group to change, people overwhelming move to a new group. It's not a capitalist or socialist thing.
I'm in the groups I am because I like the people and what they're doing. I don't generally hang out with people because I expect it to benefit me.
I'm having trouble thinking of groups of people who are even able to change members outside of modern capitalism. Through most of human history we've been stuck with our group or tribe. Heck, I see people stick with groups that are toxic to them just out of the sense of connection it gives.