IMO the problem is that web development education is often very informal, if not just straight up on the job. A lot of accessibility is to make links <a>, buttons <button>, tables <table>, lists <ul> or <ol>, etc. Append alt text as needed.

The problems come up when people see default <button> styling and then go off and make it a <div> instead. Nobody really teaches why this is a bad thing, you certainly won't find it in some random web tutorial on a blog from Google search. But if enough kludges like this happens in a code base it becomes pervasive tech debt in lots of tiny places, which is possibly the worst kind of tech debt.

I don't think it's impossible to educate engineers to do this, the problem is that we don't really educate about web development in the first place.