Why two soundtracks?

I just watched the film again and was royally entertained. Again.
The soundtrack in the movie was perfect. Lot's of oldies but goodies and several great songs by artists I had never heard of before.
When I went looking for the soundtrack album I found mostly Jerry Goldsmith's unused score.
Anyone know what happened?

The pumps don't work 'cause the Vandals stole the handles
Bob Dylan