That's not likely what caused its decline. I used Delicious for quite a while, and my reduction in use had nothing to do with what it used on the backend. I think it served its purpose as a social bookmarking site pretty well for the time it lasted. But it finally started its decline likely due to old fashioned competition. Google pretty much made the need for personal bookmarks obsolete, and sites like Digg and Reddit were a much better method of sharing links with curated lists and discussions.
It lost momentum - no features or anything added for three years.
A large number of people use computers as memory tools. Trello, Evernote, Pinterest, etc. - Google doesn't seem to be particularly relevant. Perhaps you mistake your usage pattern for everyone's?
Neither Digg nor Reddit made a way to share curated lists, so no clue what you are talking about there.
