This is all my personal experience but as I’ve gotten older, it requires more time and effort to maintain friendships. People get busy with their own lives (work, kids, moving away, change in hobbies). Sorry this post is going to be a bit long because it requires some backstory.
Some of the things you mentioned sound like someone from my friend group, I’ll call him Steve since that’s his name. There were a bunch of us who were together every weekend in our 20s, usually going to bars, concerts, or sporting events and drinking a lot. Steve slowed down on the drinking earlier than the rest of us, then he got more involved in his church which is where he met his now wife. We didn’t see much of Steve after that and I eventually moved away. That friend group still does the occasional outing and I know Steve isn’t involved in those. I remain in contact with Steve and he texted me a few weeks ago about something he wanted to do, I don’t live in town so I suggested another friend and Steve replied that they don’t hang out anymore. This was my reply to him and I think it’s appropriate here: “There’s something my dad told [my brother] when we were growing up but I always remembered it for some reason, it’s about friends/spending time with them. It was something along the lines of “somebody’s gotta make an effort or nothing is gonna happen”.”
We all still love Steve and I always invite him out with the larger friend group when I go home which he usually takes me up on. But, I spoke to the friend I suggested to Steve and she that friend said that he hasn’t heard from Steve in months.
This is a really long way of me saying that friendships require work to maintain sometimes. If you want to join in or be thought of as someone to be included regularly, then you need to reach out and start the conversation or it might not happen. If they’re true friends, they should have no problem including you again and it should be like old times. If you have force your way back in or they’re still not inviting you regularly then maybe you have just grown apart. The other side is, if you are invited, you need to join somewhat regularly. If you say no all the time, they’ll just stop inviting you again.
I almost used a different name but thought fuck it, if he were to ever read this, he knows my thoughts since we had this exact conversation