[happytoexplain]

Oh, thanks, I think I see. Before we had to think about mobile, any web page that wasn't just a block of text (e.g. inline images, side bars, etc) had bad/broken layout at small widths. Instead of waiting for the whole world to fix their websites, mobile browsers just shrank them a bit. The browser couldn't distinguish between a website that looked good and bad on mobile, so it shrank all of them. And because the web is inherently a slave to backwards compatibility, it's that way forever now.

Mobile browsers do the shrinking by messing with viewport defaults, so we fix it by re-applying those defaults.

I think the MDN doc's only mistake was describing "device-width" as "100% viewport width", since that seems like circular logic.

[marcosdumay]

> Instead of waiting for the whole world to fix their websites, mobile browsers just shrank them a bit.

What comically never fixed anything. But yeah, that's the rationale.

AFAIK, mobile browsers only actually managed to display non-text sites when pinch-to-zoom was invented and the sites started to include the viewport meta. And they only managed to display text-only sites by reflowing the contents. The shrinking the viewport era was a deep local minimum of usability.