Another reason HLS is so widely used is that the App Store Guidelines require it for video streaming longer than 10 minutes:
Video streaming content over a cellular network longer than 10 minutes must use HTTP Live Streaming and include a baseline 192 kbps or lower HTTP Live stream
It's also the only format that works with Apple TV via AirPlay.
If you're already deploying HLS to target iOS and Apple TV (natively as well as in Safari), and HLS is already supported in other devices like Android, desktop browsers via Flash, and now JavaScript, then it seems like the path of least resistance.
Video streaming content over a cellular network longer than 10 minutes must use HTTP Live Streaming and include a baseline 192 kbps or lower HTTP Live stream
It's also the only format that works with Apple TV via AirPlay.
If you're already deploying HLS to target iOS and Apple TV (natively as well as in Safari), and HLS is already supported in other devices like Android, desktop browsers via Flash, and now JavaScript, then it seems like the path of least resistance.