Ok sure, it'd be _nice_ if blind people could navigate my website. But... how nice? How many screenreaders can I reasonably expect as a % of traffic? What difference will it make to their quality of life? What decision process should I use to decide if _my_ website needs to support this? Does my personal blog to support a screen reader? What about this bank login page? This motivating information is a cruicual step in actually getting people to care enough to do something different.
A contrasting example is the discourse on "bloated" webpages being slow and hard to use on shitty old phones. The upshot is that if your website needs to download and run 1MB of JavaScript then someone viewing it on a 5 year old low cost smartphone on a crappy 3G is going to have a bad time. The statistics around how many people have bad internet motivated me to try and reduce download sizes.
It would also be nice to have a guide on convincing your boss to give you time to support accessibility.
The technical details are good (and this article is quite readable) but probably aren't the key bottleneck in more people writing accessible markup.
<edited for less unnecessary snark>