There will be an abandoned account somewhere. It still exists but nobody is checking it.
It may be an abandoned blog with no new postings. A Facebook that nobody logs in to. A former frequent poster on Stack Overflow.
They’re often being overwhelmed by spam. Spam accumulating is like dating genes by comparing the number of genes with a known mutation rate.
At an extreme the poster has died.
They make me think of moulted cicada shells.