The point of a UI library is to interface with users. If it totally fails to interface with a subset of users then it is obviously deficient to some degree. It is callous and foolish to dismiss offhand users who rely on assistive technologies. You probably have a poor idea of who they are and how many people we’re talking about. You never know when you or someone you care about will become one of them, even temporarily. You never know how far your software will reach when you write it.