Why do some websites seem to use tiny print? [closed]

Starting some time ago (perhaps with a Firefox upgrade), certain sites come up with abnormally small print -- 'apparently' 8, 6 or even 4-point print, forcing me to "zoom" for readability. I know that one can tell the browser to force a minimum size, but I would prefer not to force it, trying to allow sites to present themselves as they intend. But then the question remains: if I am seeing the sites correctly, why would they use unreadably small print?

I don't recall offhand any sites to cite as an example, but will name them here as I re-encounter them. However, I have to believe many other people have noticed this. I am using Firefox 93.0 on Ubuntu, and assume the effect is observed by all Firefox users.