I think some of this is because it's way harder to write a new library for a well-established language & ecosystem and become well-known for it, than it is to d

I think some of this is because it's way harder to write a new library for a well-established language & ecosystem and become well-known for it, than it is to do the same in a new ecosystem. This goes for languages and frameworks both—React, for example, generated tons of opportunities like this, to become known for something by basically solving a problem that'd already been solved 1,000 times—but with React. Like, if you want to build your résumé and get offered some of the cushier programming-adjacent gigs and get to present at prominent conferences and generally become A Name, how likely is that to happen if you try to launch some big web framework, or an auth library, or an ORM—in Ruby? Or Java? Nah, too crowded. But if you pick some up-and-coming language (that's up and coming in part because everyone involved is doing exactly what you're trying to do) or hook your wagon to some new framework's (or database's, et c.) hype cycle, well, now you're talking. As a bonus, many of these projects require little or no novelty—it's all well-trod territory. Just half-competently do what hundreds of others have already done, succeed at promoting it (tellingly, this is the harder part) and you're a rockstar. And hell, maybe doing all that does demonstrate some kind of remarkable and valuable skill, for all I know! But the point is, if that's the kind of thing you're trying to do, you need churn, and a bunch of people all trying to accomplish the above drives that very churn. Very little of that activity actually advances the industry, and the churn itself is a huge drag on everything.