I think it's easier to sing this way. I've been thinking about it a lot lately and it's the only reason I could come up with. "And I couldn't really care less" would be slightly longer and maybe more difficult to pronounce without changing the melody a bit.
Exactly, I feel the same about it. In a slow, thoughtful song that seems to focus on the lyrics, especially a song like The Forgotten (these were supposed to be deep, y'know?) it's much more difficult to overhear them being weak. You're kind of forced to listen to those lyrics even if you don't really want to, because there is less to focus on instead.