You have to admit that not everybody can boast of being in a particular circle of friends from the most basic group they first were part of till they became adults.
It’s not exactly practical.
Afterall, as people grow older, some values might change, some tendencies might develop, some habits might rear their heads and so on.
Some other times, locations change, interests and fields change and so closeness might gradually thin out.
You don’t need to break too much of a sweat over people who won’t keep in touch. I think when only one party is striving to keep the cord of friendship taut, it might be time to revisit how much the friendship means and how much of energy should be put in it.
Things change, people change, deal with it!
In my opinion, shared values and then physical proximity should stand above other criteria in deciding who is worth more time than others.