Earlier quoted context omitted.
You're missing the forest for the trees here. Sites are using pixels as a proxy for physical device size. Which obviously breaks. I doubt people actually intend to display mobile view on a 720px, 12" wide device. They're only working correctly if you ignore the intent and only look at the technical implementation. The technical implementation is flawed and doesn't accomplish the intent.
But the OP is using pixels as a proxy for screen size as well, they're deliberately presenting their screen as 720x1080 to make the fonts bigger because they are too far from the screen. The stupidest thing to do at that stage would be to say "ah I see you're running a low resolution on a huge screen, let me make all the text tiny".
As I read this I:
1. am wearing my computer reading glasses +1.5
2. have my browser set to zoom HN by 125%
3. am reading distance from the screen
I know programming and tech in general is a young man's game, but let's at least try not to be ignorantly ageist & ableist.