What is with these old accounts, hacking?

Some of you know already that I follow the allowed limit of jellies.
Some were gone long before I arrived. I am following some because that links me quickly to cool old questions. Some I just like the avatars so much I can’t bring myself to dump them. Really, my profile page is so pretty. Sometimes I have to weed through though, to follow new jellies. One of the things I do is look at how long the account has been inactive.
I can understand someone checking in frequently for four years and not actively being involved, but it seems to be something I see frequently.
Is someone checking into other accounts? If so, why would they do that?
Is there someone here who is responsible for over two dozen accounts, leaving some dormant a long time, but checking in anyway? Weird. I just wonder.