Accessibility is a usability issue because barriers to access are barriers to usability. If a product is not usable for people with disabilities, it is not fully usable, period. Treating accessibility as a compliance checkbox misses the human interaction dimension and produces technically conformant sites that still fail real users.
Technical compliance (meeting WCAG criteria) does not guarantee an accessible or usable product. A site could pass every automated audit and still present usability barriers that only surface during testing with actual assistive technology users. A video with captions designed for deaf and hard-of-hearing viewers also benefits anyone in a noisy environment, illustrating how accessibility improvements extend beyond their target audience. Many accessibility practices (clear navigation, consistent elements, descriptive link text, high color contrast) improve usability for everyone, especially in limiting situations. The recommended approach pairs accessibility audits (technical standards verification) with usability testing involving users with disabilities using their own assistive technology. Products fail not just because they do not function, but because they make users feel singled out or communicate that something is wrong with them. The emotional dimension of accessibility is as important as the technical one.