> Clients can't automatically fix all existing web pages, because the semantic information just isn't there

Yes it is. Webpages semantically provide information on the purpose of onscreen elements by their appearance. Vast quantities of humans ensure the semantic information is there by using the websites. Websites that do not convery semantic information through their appeareance will die, because nobody is using them.

> Not all accessibility tools are expensive

I want to acknowledge your point here - the situation may have improved the last time I looked at accessibility tools, which at the time was mainly overpriced badly maintained proprietary software. I still think the "boil the ocean" strategy is discredited and wrong.