Your experience is not uncommon. I also have a preference to stay home rather than go out to socialize. It's partly that I get exhausted from socializing too much. But a large part of it is that socializing tends to also involve spending money, which is scarce at times.
But, I have noticed a similar thing with other friends. And while I would rather stay home, I make an effort to call them or to go visit for a while. It lifts my sprits a bit to be a friend in the active sense by doing the things a friend does, like visit and take an interest in how they are doing. I've come to realize that many people are lonely, like I am sometimes, and simply need somebody to encourage and take an interest in them from time to time to bring them some contentment. I guess what I mean to say is that I give friendship in the way that I would want others to take an interest in me. But like you, I'm more selective. It's not just to anybody.