To some extent developers are a product of their customers' demands. If customers are emphasizing dirt prices ($200 websites what the hell is going on?) and launch deadlines of "a couple of hours", they aren't thinking about accessibility, along with a half dozen other things.
It's really become evident to me since web development became a focus of my career, that people remain blissfully unaware of those less fortunate than them. Which we should shame out of them in my respected opinion.
At the very least, all visual elements should include an alt tag.
Making your content "readable" is a good idea anyway.
One last thing, and sorry such a long comment, it occurs to me maybe a lot of websites aren't "accessible" because things like Alt tags would expose the manipulative subliminal tactics of the design.