Bang Bang: I Just Realized Something

I was listening to “Bang Bang,” by Jessie J, Ariana Grande, and Nicki Minaj, and I noticed something in the production which I thought was cool but also curious.  It’s rather subtle, but they added a sax or some type of horn to the last chorus of the song.  It starts around 3:02 in the clip below:

Personally, I think the horns add power to the chorus and really fill it out.  It also seems to emphasize the beat more.  So, I’m wondering: why did they only add those horns in the last chorus?  Why not every chorus?

Perhaps it’s like that old saying, too much of a good thing…