The cruelty of coercive control where you insist on trying to force people who just want to be free of you to join you in an exit interview against their will.
In this case, it actually sounds like something happened. This isn't ghosting so much as a mystery.
But it was also four years ago, time to move on.
As for the usual complaints about ghosting - another person is exercising their own boundaries. Accept this, you have no other choice. Moaning about it won't change it but it might make you feel worse.
It's perfectly normal to ghost people. Nobody owes you a second of their time or attention and can dump you for any reason at all, or none. It happens to everyone and always has. It's not a new behaviour, it just received a fresh label a few years ago.
And it's just life.
Before mobile phones and the internet it was much easier to avoid people. Nowadays, Class A Clingers have numerous avenues of approach.
I was ghosted a couple of times by friends over the years, once it was quite a painful surprise.
But I'm not an emotionally coercive person and understand everyone has a right to their own boundaries and that I have no right of any kind to demand an explanation from them or way to try to get that short of acting like a deranged stalker.
And so after being ignored for a couple of weeks,I realised that no matter what their reasons, whether fair or unfair, they owed me absolutely nothing and I would be making a completely embarrassing arse of myself by chasing after them. From time to time I still wonder.
Meh, such is life.
You cannot make anyone choose you. You can only choose how you react to that and it is desperately pathetic to cling to a person who has told you they don't want you.
And saying nothing is also saying something.
Ironically, clingers are the ones who are the most likely to be ghosted because that sort of shit is really annoying. Needy people who overstep boundaries are much more likely to be dumped with no explanation to avoid all the quivery pleading, complaints, demands and debate tactics the other person didn't sign up for and isn't interested in.
Nobody owes you an explanation. And you should be glad of that.
I think in their minds many of the ghosted imagine some discussion where they are vindicated, or the other person changes their mind, or it was all some big misunderstanding. Somehow, they will get to come out on top.
The reality is, if they dumped you, for any reason or none, that can't be fixed no matter what and what on earth makes you think it would be easier if they actually told you?
"You're just really needy and annoying and I want rid"? Or "Oh, were we friends, I never really thought of you like that, just a coffee acquaintance" Or "I hate your horrible sense of humour and that awful laugh, you smell bad, I just can't stand the sound of your voice, you're a bit of slapper, I don't trust you" or "Your husband tried to fuck me, your children are super annoying, you are incredibly boring/arrogant/stupid" - or any one of a thousand other reasons someone might dump you without explanation.
There's a better than even chance in any ghosting scenario that you definitely won't feel better for knowing why.
Or maybe the reasons are on their side. Either way, they don't owe you an explanation or an exit interview.
Least said soonest mended.
All of the ghosted must learn to accept that you must move on, and dwelling on it will only make things worse.
Moving on is literally your only option.