"no matter what"? One of the more popular uses for these immediate-mode UI toolkits is to create interfaces for video games, either debug UIs or the menus painted over the game's main scene/content. I don't think people who need a screen reader are going to be playing a twitch-reaction shooter game.
I agree that these shouldn't be used for general use applications, but I strongly disagree with the sentiment that somehow all programs should be forced to work with screen readers. Some domains and applications are primarily visual and don't really translate well to textual interaction. I think these kinds of toolkits work best with those kinds of applications.
You shouldn't use these to write the next Discord or Slack or Firefox or LibreOffice etc. -- but I don't see a problem with making a debug UI or a menu for an action video game with an immediate mode toolkit.