I am in the 'some people don't want to be found' camp.
And if people lose touch it's for a reason.
Some people are saying 'many people lose touch for ALL sorts of reasons, but IMO, most people won't 'lose touch' unless they want to, and they are not interested in maintaining contact. If you were that super-close, you'd have stayed in touch. That's the long and short of it.
Many people have had friends in the past who they were fairly close to and had fun with for a few years, and then for whatever reason, they drifted apart. Sometimes it's them who drifted away, and sometimes it was you who drifted away... But, as I said, if you were that close, you would both have maintained contact.
On several occasions, I have had old friends tracking me down and firing messages on facebook to add them as a friend, and get in touch. These were people I had in my life for 3 or 4 years some fifteen years ago, and we had had nothing to do with each other since. So I just ignored their request as I was not interested in getting back in touch. We'd got no friends in common, no family in common, and no shared history except those 3 or 4 years.
Many people just want to add to their 'facebook friends' number anyway, and will add you as a friend and then not bother speaking much after that. It's just a way to boost their friend number, and their 'likes,' and a way to brag about what they've got.
One woman I used to know at school (in the late 1970s/early 1980s,) added me on facebook some 12 years ago, and said 'hi patti long time no see.' I asked her how she was and made small talk. She went on to say 'I now live in Australia, and am sending you (via private message) 30 pictures of my house, my pool, and my horses, to make you jealous...'
Instant block. I thought what an absolute nobhead.
Then there was another woman I knew from school, who would maintain contact intermittently, (over the years,) but only when SHE had something to brag about... New car, new house, new boyfriend, new job... She would just ignore my letters and phone messages when things were not going amazingly for her. Then after a couple of years, she would write again (or leave a phone message) and say 'give me a ring, it's time to meet for a coffee!'
I started ignoring her after a few years, and SHE tried adding me on facebook some 5 years ago, so I just blocked her.
Then there was ANOTHER woman, who I met at work when I was about 23/24. She and me were fairly close for several years, and used to go out for pub lunches and drinks, and then she totally ghosted me, when I said I was getting married. She was five years older than me, and at nearly 30, had never had a long term relationship. DH figured out she was pissed off/jealous/upset. But I did nothing wrong. And didn't deserve to be ghosted. I tried writing to her and phoning her, but got no response.
Out of the blue she sent me a facebook message 15 years later. I just ignored her and blocked her.
I now do not have my real name on facebook. Like if my name is Louise McDonald, I would have it as 'Lou Mack' IYSWIM. So I can't be tracked down by ANYone.
I have everyone in my life who I want and need... DH, DD, (and her boyfriend and his close family,) my very close and immediate family, 4 very good friends (2 who I have known since childhood/mid teens, and have kept in touch with - and they have with me,) several good neighbours, and a couple of good pals at work.
I certainly don't need or WANT people from the distant past tracking me down to try and get into my life again, especially if THEY were the one who stopped the bloody contact in the first place.. Or if they are someone I knew from school (or from work 30 years ago,) and I've not heard a damn thing from them since then.
As I said, people DO lose touch for a reason. And it's because they WANT to. Yeah, there are probably accentuating circumstances in a few instances, but for the most part, people lose touch because they want to. And some people don't want people from the past tracking them down and getting in touch. As I said earlier, you'd have been friends all along, if the friendship was meant to be.