[somat]

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.

[perilunar]

As mentioned above, adding a viewport meta tag will make most unstyled pages look much better on mobile.

<meta name="viewport" content="width=device-width, initial-scale=1.0">

> Why are mobile browsers defaults so wrong?

History. When mobile browsers first appeared they had to default to a desktop page width to avoid breaking exisiting content, much of which was either built in layout tables or used CSS that assumed a wider window. The viewport meta tag was introduced (by Apple in Mobile Safari when the iPhone first came out, IIRC) so developers could override that behaviour. I think the defaults made a lot of sense at the time, and Apple made the right choice.