Growing older makes certain people more valuable because history becomes harder to replace.

People who knew you before are irreplaceable in a specific way. Nobody new can be given twenty years of shared context, and as time goes on the number of people who remember a particular version of you only decreases. That scarcity is what makes old friendships worth effort out of proportion to their convenience.

Call the person you have been meaning to call. Old friendships do not usually end, they lapse quietly through neglect. The maintenance required is far less than the value, and it is nearly impossible to rebuild once lost.