Q: help?

I recently just purchased an iphone 6s plus 16gb using current up to date software at iOS 9.2.1, when purchasing my phone i bought it from at&t brand new full retail price and i use the go phone services with it (not sure if this would have anything to do with it?). Upon starting it up and activating it and all that stuff i noticed there was no imovie or garage band or anything like that. I then go into the app store and i see that they have a cost to purchase them. Now i may be wrong but i thought they were suppose to be pre installed apps ready to go?... Just really wonder if you actual have to purchase them if they are supposed to be "pre-installed apps"? i appreciate any help, thanks.