Q: Why doesn't Apple add Sirius xm and Amazon prime?

likely because both are their compatitions and I doubt they really make money on selling appletv's but make up for it when people who buy appletv's use them to buy stuff from itunes store rather then their compatition

?

anyway these forums are user helping users so nobody knows for sure and apple will not get your advice here as they dont read the forums so if you want to pass on your words of wisdom use the feedback channels its the way to apples ear

http://www.apple.com/feedback/

The content holders all required the re-seller services (iTunes, Amazon, Google, etc) use DRM to encrypte the files so by default they can then only be played on specific devices for that service.  So Amazon DRM'ed content will not play on Apple devices, and iTunes DRM'ed content will not work on say Android devices.  It is a huge legal thing to be able to support content from other DRM'ed sources and since those sources are competitors any way there is not really any motivation to support this.