Accessibility is a factor that has traditionally been on the margins of SEO and web development. There are solid business reasons for why accessibility should be a top consideration. Accessibility can have a positive effect on sales and SEO.
Accessibility Should Not Be an Afterthought
The recent WordPress 5.0 release brought the issue of accessibility to mind. Accessibility was addressed by a plugin instead of being a core part of WordPress. This gave the impression that accessibility was treated as an afterthought and not a core requirement.