Oh dear.
Oh dear.
I get it, it's not the most cinematic experience but who actually wants to hold their phone sideways while scrolling through a feed, or switch apps etc? It just doesn't make sense to do it any other way. Also as most video is even filmed in portrait mode.
A sad reality.
I think one day phone cameras will have square or cross-shaped sensors and you'll be able to easily shoot landscape video while holding your phone vertically.
For viewing, I think it isn't the physical rotation of the phone that is a pain - it's selecting the full-screen option, or the rotate controls. The latest Android makes this better, but I hope in future apps will just play landscape videos in landscape irrespective of the phone rotation.