Why Apple's Late Push Into Streaming Music Won't Be That Easy

Apple is expected to show off its new streaming-music service later today at its annual Worldwide Developers Conference. The stitched-together Spotify rival will combine disparate parts of Apple's music operation: the mega-successful iTunes download store; the less-successful Pandora-style Internet radio service launched in 2013; and the streaming subscription service built by Beats Electronics, the headphone maker bought for $3 billion last year.

Apple is late to the subscription-music game, and building a successful streaming service is essential if the company that gave the world the iPod wants to remain relevant in digital music. These four charts show why Apple needs to make a splash in streaming—and why it won't be easy.