Encrypted video playback is/was a big reason as well. The browser wars for HTML5 EME for playback of encrypted content is still crazy, but only very recently been slightly manageable.

Safari - only FairPlay encryption through HLS, but only modern versions of Safari; Chrome - Widevine Dash, IE - Playready Dash (and smooth), but only recent versions, Firefox only after version 52 do they finally support Widevine Dash, otherwise no EME prior to that.