I think of it more as a set of skills that needs to be maintained, and is easier to do when regularly engaged.

There was a comment recently that I really liked, here, by @RBWells@lemmy.world :

I think people do not recognize the immense value of weak interpersonal bonds, like going to the same corner store all the time. But they are the glue that holds society together. It’s not the deep friendships, you can only have a few of those. It’s those people you are acquainted with, and look forward to seeing, people you wave to, all those little connections add up.

The little weak bonds help keep you grounded so that you can tighten and bolster the deeper and more meaningful bonds. I'm a better friend to my closest friends in large part because I have the experience and lessons learned from past situations with friendship: how to be supportive when a friend is going through a death in the family, a divorce, a period of unemployment, how to celebrate with a friend getting married, having new kids, etc. Each little situation presents an opportunity to be a good friend (and gives better information about what you can expect from your good friends), and just basically sharpens those social bonds and your ability to navigate them in a way that enriches your own life and your friends' lives.

So it's not a finite amount of juice. It's a muscle that can be made stronger, and I'd argue is worth actively making stronger.