Yep as someone who's done a significant amount of front-end development ARIA and accessibility is more billable hours, more time involved into project, and more testing. When it's my own consulting I literally add it as a line-item to the bill and let customers take it off if they want to save cost, and when it's for professional work the only industry that has actual regulation around it is education/government.
Truth is most companies are pushing the cost of development down however they can, and to cater to the accessibility market you're sinking significant dev/testing time into doing it right. Also, you can't blame me in a capitalist society for dropping this on the floor when my customer/employer wants me to... in most situations the hours invested into accessibility will never turn around into profit.
The other problem is I do accessibility right. And most devs don't... I'll actually go through and do UIX experiences on-screen, then replicate it "blind" using a screen reader. This testing/tuning takes real time. Like - I can go through and do best practices with ARIA tags, well thought out HTML5, etc and still it's a total cluster once you actually use the application.
It very much may not be "ignorance/difficult" - looking at what this dev has accomplished with this editor I'm going to give them the benefit of the doubt and say it was just extra time for a tiny fraction of their audience that they haven't invested yet. Harsh reality is they may not have that budget of time to go the extra steps for something as complex as this.