You're limiting the scope of ppi to desktops only? Almost ~80% of the web is on mobile [1][2][3]. Close to 56% people online are "mobile only", which means that they will never look at anything other than a hdpi screen in their lifetime.
[1] https://hostingtribunal.com/blog/mobile-percentage-of-traffi...
[2] https://www.statista.com/statistics/277125/share-of-website-...
[3] https://www.smartinsights.com/mobile-marketing/mobile-market...