I think the main difference is that when you and your friends live near each other (and/or work together) and enjoy the same sorts of activities, maintaining th

I think the main difference is that when you and your friends live near each other (and/or work together) and enjoy the same sorts of activities, maintaining those friendships (even at a deeper level than "hey let's go to the club and hang out without much real social interaction") isn't too difficult. When people get married, change jobs, start families, move away... then it actually requires a solid amount of effort to maintain those friendships. For some people they really value the friendships enough to put in that work, and for others they don't (and when they do, it has to be mutual for it to work out). The sad part is when people value the friendships, but don't understand that shift, and what's required, and those friendships fizzle out. I still maintain friendships with a 10-15 people who no longer live near me, and who are doing different things with their lives, and are in very different circumstances than I am. The oldest of these friendships are pushing 30 years now. It's doable, but everyone needs to be on the same page as to what they expect from and what effort they're willing to put into the friendships.