Foster, that's exactly the reason!!
Also, b/c Shaiman said that the song doesn't establish anything that wasn't already set up in Good Morning Baltimore. With movies, you need to keep the pace moving more quickly.
I really wish I could remember where i read this interview. I'm sure someone else out there has seen it. I'm pretty sure it was on a Bway related site.
Oh, and he also said they wrote 2 new songs, including a ballad for Tracy late in the show.
....but the world goes 'round