worthless when the website itself decides thatbit won’t show you the content

Businesses are legally bound to make their online content accessible: a screenshot without alt text doesn't solve this for them. Isn't it common practice around here to link to archives? Quoting & linking isn't worthless.

quoting? you mean, all of the response tweets?

Yes. Unreasonable? No, compulsory & common standard industry standard. Out of legal necessity (and market reach), they already write text out (as alt text for all meaningful images). An image of a tweet with replies requires writing all that text out.

Try this exercise yourself to realize how pointless an image of text is (which images of tweets mostly are). Take an image of text, write the markup to display the image, include an alt attribute set to the full text shown in the image. If you have any sense, you'll return to the source of the image to copy & paste the original text into the alt attribute. If you lack sense, you'll tediously read the image and retype it into the alt attribute. Your choice.

Realize anything yet?

1. You're returning to the source, so linking it is basic sense, right?
2. You already write text out, but your effort is wasted as a flat text attribute for an image that adds nothing compelling, only some meaningless visuals of UI artifacts. That text could instead be the main attraction with semantic mark up (blockquotes, paragraphs, lists, etc). It makes more sense to skip the image entirely & quote the text directly: less work, more functional, better.

and how do you quote images, videos?

The way it's already done. Online news doesn't typically give screenshots of images or videos. They link, embed, or copy the image or video to directly provide it alongside some quotes.

Selecting lines of text instead of rectangles of screen to copy & paste isn't a novel, farfetched idea.