They aren't as the rendering of a website is ultimately always controlled by the client/visitor.

Any website whose semantic is only made of text is infinitely more accessible than another that would use bigger fonts but would include images or content that only render if javascript is activated.

And ultimately, they have every right to make it the way they want.

> Washington Post are using 20px (and those are usually longer reads)

In the full text maybe, I find much smaller fonts than those on computer.rip in metadatas and subtitles.