This doesn't follow. It's an argument for "put black text on a white background and call it a day because this is too hard". People don't pay money for that.

Web fonts solve an entire class of problems unrelated to whether the user is standing in the sunshine or not.

> Nobody tests their web fonts as thoroughly as the default fonts have been tested on their respective platforms and devices.

This is wrong in fact, given that the most popular fonts are coming from big design houses that probably know more about the details of font rendering than I'll ever know about any subject [1]. It's also wrong in principle because exactly zero people get paid to test platform-default fonts for my application or website. That leaves it up to the developer to test the site on every platform under the sun and moon and, even when they do that, they still have users with goofy font installations that make it look bad or unusable.

> Using the default fonts guarantees you'll never have to worry about such bugs.

Again: it doesn't, because when you do this, you're using whatever fonts are installed on the user's system, and there are a lot of people running around with crappy knock-off fonts installed. Using the default fonts guarantees that this is an issue.

And where are these people coming from that care about inconsistent subpixel rendering in web fonts but don't care about inconsistent layouts from using whatever bag of fonts they happen to have on their system at the time?

> The system's installed fonts are guaranteed to work.

Allow me to repeat myself: a "Consolas" font on one system is not the same as a "Consolas" font on another system. There are no guarantees when relying on a system's default fonts, and that's why web fonts are popular.

> ...Wordpress, and many others use the system fonts.

It's a shame you included this example, because it opens a big door for me.

Let's look at the style.css file for Wordpress's default "twentytwenty" theme [2]. It includes a gnarly font hack near the top along with the following comment:

> Chrome renders extra-wide   characters for the Hoefler Text font. This results in a jumping cursor when typing in both the classic editor and block editor. The following font-face override fixes the issue by manually inserting a custom font that includes just a Hoefler Text space replacement

...and right below that it includes two web fonts.

Their twentynineteen theme includes the same hack but no other web fonts.

How about the most popular third party theme? Web fonts: https://themes.svn.wordpress.org/astra/2.4.4/assets/fonts/

15 out of the 20 most popular Wordpress themes include web fonts (not counting FontAwesome or other symbols-and-icons fonts). I checked.

Facebook, Github, and Twitter operate at scales that are not relevant to most of the engineers on HN. They are motivated to spend engineering budgets on performance and they're willing to forsake things like typographic consistency if it saves them having to pay for another data center.

The first not-Facebook-scale example you cited is full of web fonts.

[1]: https://fonts.google.com/?sort=popularity

[2]: https://themes.svn.wordpress.org/twentytwenty/1.3/style.css (warning: content-disposition: download)