When a screen share takes over, a conversation turns into a broadcast, which isn't always what you want.
There will always be scenarios where the improved resolution of a screen sharing codec will be necessary (and nothing is stopping you!), but I find a lot of the time there's a big white screen with a bit of branding and one bullet point on screen, and I can't see the face of the person who is talking.
I was on a group call recently where the speaker presented in this way for half an hour as a tiny thumbnail and I found it quite painful, thinking "I've been listening to this person for ages but I wouldn't recognise them in real life".
Sure enough, a couple of weeks later I had an awkward conversation where this exact person kinda recognised me but I didn't recognise her, so I felt pretty vindicated .
If we avoid the overhead of screen shares, the conversation flows a lot better, and everybody can be seen without the host having to turn anything off. And don't forget, if somebody's on a phone screen then they can't see all the detail anyway. This is why I prefer zooming in on important content than sharing my whole screen (I zoom in on my desktop using a pinch gesture in Video Pencil on my iPad and it feels magical).