Cost, knowledge deficit of the designer &/or eng side, inertia.. there are a lot of reasons. Many html a11y features are as easy to implement as adding an attribute (but people are unaware) -- other things, like designing a product flow to be accessible, can't be fixed with engineering; they have to be redesigned.
My team at LinkedIn is trying to solve the eng side of this with a combination of automated tooling like linting & headless testing, reporting, etc., trying to make it as painless as possible for an engineer to fall into a pit of success re: a11y for web/mobile experiences.
Not cost of implementation, I don't think. Maybe cost of "lost value of data and advertising they could collect".
Do you think it's more expensive to implement a few accessibility features their site had with little effort in the 90s, or to fight a case to the Supreme Court, as in the case of Domino's?
