Song Sequels

Everyone hates it when Hollywood ruins a perfectly good film by allowing, and in some cases insisting a sequel be made.
See: The Matrix.
It doesn't happen that often in music but occasionally a band will follow up one of their massive hits with a sequel. I can think of a couple of examples.
Britney Spears did it twice: Oops, I Did It Again was a direct rip off of Baby One More Time, but the sequel to that debut hit of hers came when she recorded a song called Stronger, with lyrics like `My loneliness ain't killing me no more'.
Metallica did it with Unforgiven II, which was a follow up to, in my view, one of their best songs `The Unforgiven'. The sequel in that case was a good song in itself and retained the feel of the original but wasn't as good.
Anyway, this topic came up when I picked up a CD by a band called The Rasmus, who you may recall had a big hit a few years back called `In The Shadows'.
It's lyrics included: `No sleep no sleep until I am done with finding the answer, Won't stop won't stop before I find a cure for this cancer, Sometimes I feel I'm going down and so disconnected, Somehow I know that I am haunted to be wanted, I been watching I been waiting in the shadows all my time I been searching I been living for tomorrows all my life.'' Good song.
The sequel is a song called Night After Night (Out Of The Shadows), with lyrics including: `Still disconnected, and unprotected, still I'm haunted but unwanted...''
So the question is, are musicians running out of ideas - or did they have such a big idea it had to be two songs - or did they feel the need to either back up or rebuff an earlier song?