What is the reason when people suddenly stop posting altogether?

I am not talking about general users or trolls
(since they don't project themselves deeply into the community)
but among those who post daily life updates
and share sweet stories about their wives and children,
using this place like a personal diary,
what is the reason they suddenly stop one day?
It is not that they become less active because they are busy.
If they simply got tired of the community and decided to quit naturally,
their frequency of posting should gradually decrease
before they eventually leave.
But for those who post consistently without any change,
only to suddenly stop one day
and not log in for over two years afterward,
did a major family crisis occur?
If they were caught using M-Park by someone around them,
they would at least delete all their posts before leaving.