Okay, iTunes/Jonas Brothers/Zoey 101 question here! (SOUNDS CONFUSING, BUT REALLY, IT'S NOT)?

Okay, so I am on iTunes, and I heard that the Jonas Brothers song 'Mandy' was on the Zoey 101 album. I typed in Zoey 101, and clicked onto the CD cover. I immediately wanted to purchase the song when I saw it on the list. However, it also said that you have to buy the whole album in order to get it. I mean, it won't let you buy just one song seperately. Why is this?