"By this logic, the most developed language ecosystems should be those built from languages which are the most difficult to develop for." It only implies that

"By this logic, the most developed language ecosystems should be those built from languages which are the most difficult to develop for." It only implies that the relationship between difficulty of development and developed ecosystem is not monotonic. It's actually fairly normal for two parameters to be highly correlated to each other along most of their range & domain, but for the correlation to suddenly fall apart at the extreme. (I think there's a term for this, and I'm wishing I could remember it, so I could to pages I've seen discussing it. If anyone knows, links solicited.) Of course, the real problem is that there's almost certainly a lot of such parameters, and having what may be merely a "just-so" story for Lisp's general failure to set the world on fire and it's excessive power may not be particularly determinative of anything. It does at least fit the facts. Most of the other possible answers have at least had the seed of a solution created (e.g., package manager solutions), and it still hasn't taken off, suggesting that wasn't the problem. (Though we can't eliminate the possibility it needs multiple such things.) The fact that Clojure seems to be settling into a C-list language position after its push also is suggestive of it not being any of the things that it fixed.