With videos, subtitles/captions are useful for deaf users, and useful for blind people when a video has no narration, just a soundtrack.
I say the reason screen readers are given a higher importance than unusual or outdated browsers is a matter of being able to choose. When you use an old browser, you can choose to upgrade. When you have a disability, you can't choose to not have that disability: you're stuck with screen readers until a better way to browse the web with your physical constraints is found.
high accessibility overlaps heavily with effective white hat SEO. The goal of accessibility is to make web content accessible to as many people as possible, including those who experience that content under technical, physical, or other constraints. It may be useful to think of search engines as users with substantial constraints: they can’t read text in images, can’t interpret JavaScript or applets, and can’t “view” many other kinds of multimedia content. These are the types of problems that accessibility is supposed to solve in the first place.
/college roommate was legally blind; husband's grandparents met in a high school for the blind