Back in "the day" couples weren't expected to become practically one person. It was expected that the commitments required of marriage and raising kids could take a back seat a couple times a week for men to hang out with their friends. So when one person got married or had a kid they would still show up on the regular and the friendships and friend groups would survive because that wouldn't interrupt the friendship.
There are no more hours available in the day or week than there were back then so when we prioritize something we inherently de-prioritize other things.