Delicious was a social bookmarking site, not a bookmark synchronisation backend.
For me it was the communal curation effect.
Find someone else with an obscure site or tag and check what else they have saved. It was a deep, deep rabbit hole.
The new owner is the developer of pinboard.in. The pinboard API was modeled after del.icio.us, so it might just be a data import into pinboard exercise.
Maciej Ceglowski owns Pinboard. Perhaps, opening it up again will make using Pinboard more attractive. He could use it as a form of upselling