Glad this thread is still going. My boomerang at the beginning has become a vanisher. Yes, still get those WTF moments often, actually, every other day. The problem is right there, Treasur, the way they left us. Cruel beyond belief.
My take on it is because they are cowards, can't face their problems, and can't face giving others bad news. Can't face other's pain, especially if they caused it. That goes for their own kids, too. Can't face problems in general, that's why so many of them are penniless and indebted. They run from the truth, thus increasing their debt and making it harder for them to be able to clear their debt ever.
They are immature, believing that if they ignore problems, they might disappear. When faced with problems, they feel like victims, like they're so unlucky, or that others have forced them to cause their own problems. I believe the vanishers have this kind of personality.
They look for quick fixes. We are told that all the time, but I can relate it to their money problems, too. If they can borrow from a relative to keep going, they will. I call that a quick fix, too. It just increases their debt. I use the money example because my H is one of the extreme replayers, spending and spending to please OW, not paying off any debt, risking going to prison if he doesn't start paying maintenance by the end of 2019. I'm sure he has a plan for that, probably running away to some foreign land, as if there's anywhere to run any more. You can be found everywhere these days.
Comparing my H's quick fix system with his finances to how he is living his personal life, OW/spending/avoiding me and kids, helps me see it as a general problem in him as opposed to a personal refusal of me. We are told it's not about us, they did not reject us, and I know this to be correct in principle, but I do have to keep reminding myself. With a vanisher it's so easy to feel that they really did never love us and our marriage was a mistake. With a vanisher, you don't ever get a crumb like with the clingers, although a clinger drive your emotions crazy.
Coming to the forum helps me rebalance myself. There's comfort in hearing I'm not the only one living in this WTF world. There's no comfort in RL. I can't tell anyone in RL how I really feel, and you all know what I mean. Thank goodness for this site.