Sure, but what I'm arguing against here in this thread is the pervasive "Mozilla is evil, they only killed XUL extensions for fun". Just read this thread.
When actually millions of users get a vastly superior Firefox. Many, many extensions have been updated. And some extensions – mostly niche ones haven't. I love that trade-off.
On this, I definitely agree.
The point of your post on which I disagree is the idea that we need to name a "culprit".
Parent started blaming people. I certainly understand when authors don't have time or have lost interest.
Insofar I was wrong. It's not authors who are to blame, it's very vocal users. You can see a few of them right here.
Porting an add-on to a whole new architecture is lots of work. People who do this on their spare time, or small companies, or companies relying on contractors, may not have the time/resources/will to do it, even within two years. Also, in some case, the APIs are simply not available.
As for why I believe that the move to WebExtensions was necessary and could not be postponed further, I have written a few lines in another thread: https://news.ycombinator.com/item?id=15695854