You obviously don't understand marketing.
If I give you a $100 item for free for buying something, I'm NOT out $100. I'm only out what it costs to make that item, like $50. Your perceived value is $100, but my cost is $50.
If I gave you a price reduction of $100, then my cost is $100. Not as good for me.
Additionally, Apple gets more people using Beats and can talk about those increased numbers. They can't do that if they just give cash back. And giving $50 off sounds worse than 'free $100 beats'.
This is why so many stores, like Target, want to give away $25 gift cards with $100 purchase instead of just $25 off. First, it encourages people to come back to Target, second that $25 really doesn't cost their bottom line $25.