It is for sure easier to do things wrong, but if you check at most of the major libraries for front-end (drag-and-drop, routing, dropdowns...), accessibility is built-in, and a critical selling point (e.g react-router, downshift...).
I think the proportion of front-end developers knowing about accessibility is just low, and the result is more visible for JS-heavy websites/webapps, but this is imho an education problem, not an ecosystem issue.
Having worked in agencies, accessibility was always treated as a second-class citizen (by clients or managers, not by developers, trying to push for it), and clients would often say "let's go live without it", then would come back to us asking to finish the job once they saw their competitors got sued for having an inaccessible website.
So JS may be a catalyst, but not the root of the problem. It's our job to push for the importance of it, as we pushed for responsive websites a while ago.