Note: simple does not imply useful. Plenty of great content out there that strongly benefits from telling the browser not to use the extremely limited "web safe

Note: simple does not imply useful. Plenty of great content out there that strongly benefits from telling the browser not to use the extremely limited "web safe" fonts, or incredibly ugly OS defaults for non-latin content. Let along fonts for typesetting maths, or diagrams, or even smart things like "temporarily showing scribbles instead of real text, until everyone's clicked the "ready to share!" button on their shared page experience". This is the nuclear option: it's simple, and also ensures a terrible experience of a web with content based on the fact that webfonts are going to work.