Can I respond with another quotation?
George F. Will said, "It is extraordinary how extraordinary an ordinary person is."
And you my dear are extra ordinary.
Coincidentally, not long ago a friend of mine asked me why I stayed in touch with former co-workers. Although I didn't have an answer for her at the time, I strongly suspected it had more to do with maintaining business contacts than maintaining friendships.
It's true. Networking is a drag, especially if you have to go to events and slap on a name tag and shake hands with a load of folks you'll never again meet. I think that's why I remained in touch with former co-workers. It's just easier to drop a note, ask how they're doing, and if there's a job opening that suits me maybe they'll tell me about it.
Some, of course, could sense the underlying reason and others made me feel as if I were chasing friendships, so I've learned to abandon those ones.
Networking means that you have something of equal value to offer and because I was freelance for a decade, there was nothing of value that I could add to their career. That's likely the real reason I've lost touch. I hear from colleagues every once in a while when their contracts end and I feel as if I only matter to them as a source, and an incidental one at that.
I can't say for sure what's behind the sudden withdrawal of contact with some of the people you've mentioned because usually when we guess at these things, we're completely off-base and the real reason/explanation is so different that our assumptions.