The relocation point is interesting. I have a lot of friendships that are in 'good friend' territory when we're in the same place, but otherwise go dormant for long periods. I'm ok with this and generally don't feel a need to try to change this dynamic with people. I guess they aren't close friends in exactly the way that you're describing, but they are definitely a lot more than acquaintances.
In a strange way I even feel that it can be a testament to the strength of the underlying friendship that we can pick up where we left off after years of minimal contact. I'm actually grateful for these kinds of relationships. I really don't have the time, energy, or desire to keep up ongoing text/email/social media conversations with all these people, but when we are able to meet up I have a great time and find it hugely valuable.
> we can pick up where we left off after years of minimal contact
Sure, but you have to actually do that from time to time.
I've lost count of the number of people I thought I was really close with who moved away insisting that they would keep in touch, and then I never hear from them again, ever after reaching out.
(Having kids is another reliable "friendship"-killer.)
Yes, I've never had a friendship survive a relocation. Not to say that I dislike or resent any of these people at all; we simply never talk anymore.
Kids could possibly do the same especially if your friends are not also having kids at the same time. Kids can also easily contribute to the making of new acquaintances (parents of other kids) as well. These might turn into friendships, or might fade out quickly once the kids' interests diverge (or they grow up and leave the nest).
I think I'd count those "dormant but not dead" relationships as good friends, myself, provided that we end up seeing each other semi-regularly (say, minimum every couple years or so).
In a strange way I even feel that it can be a testament to the strength of the underlying friendship that we can pick up where we left off after years of minimal contact. I'm actually grateful for these kinds of relationships. I really don't have the time, energy, or desire to keep up ongoing text/email/social media conversations with all these people, but when we are able to meet up I have a great time and find it hugely valuable.