@thalassa
I don't know why in this particular instance.

Sometimes authors get negative comments or harassment, which sucks. So they could leave their works up for fans to read, but separate themselves from the works so they're no longer getting grief about it.

Or maybe they've moved on to other fandoms, other works, they might not like this particular work of theirs, and prefer not to claim it any more but still want it to be available to others.