I highly recommend installing an extension that hides the home feed and sidebar recommendations, which at least makes YT non-distracting again.
Since a phone can show portrait or landscape videos in fullscreen (just hold the phone vertically or horizontally), it makes sense to shoot in whatever orientation fits the content or situation best.
The real problem is that computer monitors don’t easily offer orientation switching :)
The phone camera sensors often have a aspect ration of 4:3 but the sides are cropped in software. So the videos just get mutilated because convention.
Though at least 4:3 format is making a come-back because it is the prefect comprise format. Looks great on a tablet, is usable in both landscape and portrait mode. On Desktop it leave space to read comments. Perfect for youtube videos.
I'm with you there. It's the same for shooting still photos.
...but that doesn't stop people from shooting portrait video and then constantly panning back and forth because the whole (crowd, landscape, giant sea monster, whatever) doesn't fit in the frame.
The first world had a lot of computers, video cameras and horizontal screens in general before they had smartphones.
I think it plays a part.
Pausing a Youtube video overlays the video with a row of more video recommendations.
So if I'm pausing the video to see something in the video, video thumbnails are in the way.
This happens in the Roku app and sometimes in the desktop browser, but for some reason I couldn't trigger it when I tested it just now. Maybe one of my extensions blocks it.
I gave up this fight a decade ago, can't believe people still struggle with this concept.
Gaming on mobile phones, even MOBA games and first person shooters, seems quite popular here. For me, it's unplayable.