I've had 3 situations like this!
One ghosted me after I had my second child, a girl. She had a little boy around same time as mine through IVF. I think they wanted a second but it didnt happen and being around me with new baby probably too difficult which I do understand. Recently our boys now joined the same secondary, I saw her and we were perfectly friendly to each other. Friendly but not friends.
2nd friend, college friend, got on so well that she was my bridesmaid. Didn't get along with my sister which is fine as she can be difficult! I don't know if that or another reason but she just slowly sort of became distant. I didn't attend her wedding as I was heavily pregnant with a high risk pregnancy. I did send one of the nicer gifts off her gift registry and all was fine but didnt hear from her. I recently asked a few other college mates and none of them heard from ger, doesn't appear to be on SM, at least not under her own name so its sad but thats that 🤷♀️
3rd is the worst. Lifelong friends, has become distant for no apparent reason. Tried to work it out. We dont live close by so rarely see each other but chat alot on phone/text. Texts are one or 2 sentences which before were essays. DS Recently started a private school, she doesn't agree with private education, I have no idea if thats a factor! In hindsight, she didnt attend my Dad's funeral a few years ago despite knowing him all her life. My Dad & her Dad lifetime friends. Seems to prioritise other friends over me. Its very hurtful, she can be a bit moody, I have asked her twice to please tell me what's up, or even if she cant say just that some worries or whatever but no insists all is OK when it clearly isn't 🙄
I think some friends just come and go, another friend of mine believes its generally rooted in some kind of jealousy/envy. Maybe she's right.