I disagree with your disagreement, for example HN is readable but the linked site feels too small for my eyes on a 21.5" 1080p monitor. It also doesn't respect browser preferences, unless you enforce a minimum font size (which can break display elements on other sites):

  font-family: Calibri, Candara, Segoe UI, Optima, Arial, sans-serif;
  font-size: 13px;

If the dev wanted a similar effect by default but be more accommodating, they could do:

  font-family: Calibri, Candara, Segoe UI, Optima, Arial, sans-serif;
  font-size: 0.8125rem;

There's no reason why you couldn't have smaller font while still respecting browser scaling. However, they might also want to just leave it at 1 rem and let the folks that prefer higher information density to customize their own browser settings, since those are what most well developed sites should respect and it might be more accessible by default on most devices (for my eyes, at the very least).

As for targeting specific screen sizes for non-standard font scaling, media queries also would help!

In regards to missing information dense pages, try changing your browser font settings, it might actually be quite pleasant for you to see many sites respecting that preference!