A page like this, with minimal styling, the whole point is the author does not care, the author expects the user's agent to style the document optimally for it's dimensions., the optimal in responsive design. this was the original vision for the web, the agent supplies most of the style.

Except it does not, for some weird reason unstyled pages like this which should look great on mobile look like ass. Why are mobile browsers defaults so wrong?

This hits hard because this is how I build my pages (you can probably tell I am not a front end designer) I just want to put well structured content out and let the users agent display it in the manner that suits the user best. And it mostly works, it will not win any awards but it looks fine. Until someone asks why it looks like the dog's breakfast on mobile.