Why do rock stations play Crazy Train and never Diary of a Madman?

Question

Diary is a much better song than Crazy Train and they never play it. They suck

Answer 1

For the same reason they only play "I Want You to Want Me" by Cheap Trick instead of something else. Crazy Train is deemed to be Ozzy's biggest hit by mainstream America (they used it in the intro to his MTV show). So, that's what they'll play.

Answer 2

because most radio stations are told what to play by the corporation that owns them...