There are a lot of non high dpi devices out there. The majority of screens are. Whether it's your personal one (and you can't or don't want to change it) or a professional one (and your company may not want or be able to justify changing dozens of screens), you need to use them.
It's possible to display properly and cleanly on them, everyone else does it. It's not as great as on a high dpi obviously, but it's perfectly sevicable for its need.
Apple with osx is the only major os that fails to do it, either through incompetence, malice or just pure disdain for their users facing that scenario.
It’s because of cost involved in maintaining the code that can push the hinting through the various layers of the graphics stack. Coupled with Apple’s culture of ditching old technology at the first opportunity.
As opposed to what other year? Color me naive, but I thought it was supposed to be the function rather than the form that we were supposed to make those kinds of comparisons about. What about a low pixel density is /not/ appropriate to the year 2020?