Design Archaeology: Why are Closed-Caption Font Sizes the size they are?

Sometimes you can discover different points of view from the tiny differences in the way things are done. For example, with a bit of inspection, you can figure out that US Closed-Captions are designed primarily for profoundly deaf people. UK ones are designed primarily for people who lose their hearing due to aging.

How do I know this? You can figure it out from the minimum default font sizes used in the specs. The US font sizes roughly mirror newsprint sizes (what would be 10pt at normal newspaper reading distances, scaled up for typical screen viewing distances). The UK ones roughly mirror low-vision adult font sizes, and usually your eyesight goes at about the same time as your hearing.

The UK ones help a larger number of people, for what it's worth, because if you're profoundly deaf and have good vision, you can still use the UK ones.

If you flip it around, it doesn't work - the US font sizes help much fewer people because they don't help people who are hard of hearing and who have low vision, which is a large percentage of the elderly.

This means that the US ones are bad design - or at least, made poor compromises. (Although it's less of an issue today because you can increase the default sizes).