You can increase the font size if you have trouble reading. Scaling the whole UI makes everything bigger, including elements that you don't read. Also depending on the OS scaling can be implemented more or less well and efficiently.
Unfortunately, Mac (integer scaling) and web (with the takeover of 1px[*]) have driven this UI concept that everything has to be scaled up for High-DPI screens. And early Gtk+ 2.* versions would gladly take any font size and resize UI elements so the label fit.
[*] though in all honesty, 1px as a relative measure of angular size is fine, it's just very badly named — I was hoping web designers would switch to ems in early days of the web, allowing users to control everything through font size directly — but that would still require some smartness not to increase padding too much with large fonts: basically, we'd want something like flexible spacing a-la TeX's hskip/vskip/hglue/vglue but catering to the screen and nuances screens possess.
Almost no UI (including web pages) is designed to work well with custom font sizes today. It's a definite win of form over function, or at the very least, recognition that designers are unable to design truly fluid/responsive interfaces that they like the look of.
Gnome still allows you to make use of gnome-tweaks to adjust just the font sizes, but you still run into issues because spacing can be too small (thus I tend to run with 125% scaling and 1.4-1.5x font sizes on HighDPI screens).
