> we don't legally require every that everyone who posts an image on social media include a written description

Not that it takes too much away from your point, but I've experienced an interesting gap in this example. While not legally required, big chunks of the short-form-text fediverse (Mastodon/Pleroma/…) have had circulating posts recommending descriptive text for image posts, and I'm actually surprised by how many people get into the habit of complying naturally—perhaps because there's also an easily-noticeable slot in the UI for it? Ten or so years ago I remember it being like pulling teeth to explain to some people doing media projects on the Web that this kind of accessibility was important, and now with what seems to be culturally a similar crowd… huh, y'know?