iPhone wants to be the most secure platform out there, so it doesn't allow external files from other operating systems to get into its system and cause problems to their user. Another reason is that Apple wants to ensure you're listening to songs through iTunes. That's why it requires you to buy songs or go through a long process if you already have them on another device. If Bluetooth is permitted, people can easily send music files from their android phone, and they won't have to buy them from iTunes. This way, everyone can get unauthorized copies that will hurt Apple sales a lot. These are the two reasons why I think they disabled file sharing between operating systems through Bluetooth.