I always though the golgafricians died off.

They did, they deported all the telephone sanitisers and then they died from some infection they caught from unsanitised telephones.

No, in the novel it's the neanderthals who are dying off. Arthur is trying to teach them scrabble to help them compete with the Golgafrinchams. Not sure how that was supposed to help the neanderthals, but good on him for trying to do something. Anyway, Ford points out that it's too late to help them. By coming to Earth at all, they screwed up the program. There was no way Earth would have given the right answer even if it wasn't destroyed by the Vogons when it was.

Earth was supposed to be the greatest supercomputer ever, but some of it's critical components were ripped out and replaced with middle-managers and telephone sanitizers. Ford supposes that that's why the answer and question don't match. Others have suggested that Arthur actually pulled the right question with the scrabble tiles and the mismatch between the two actually shows there is a fundamental flaw in the universe. The reason everything is so screwy is that the universe, at the most fundamental level, just doesn't make sense.