[stutonk]

Worse is better/creative limitation/blub paradox: Smalltalk, like Lisp, is too powerful; you can do essentially anything you desire in a bunch of different ways. Too much flexibility makes it harder for a clear use case to emerge and having too many choice points only makes pathfinding through the solution space more difficult unless you've made a bunch of firm decisions beforehand. Other languages like Go or Python make many of these decisions for you. It seems like the ideal pattern in these ultra-expressive languages is to construct a much more restricted DSL which can ultimately lead to a proliferation of completing solutions a la the JS ecosystem.

Inner platform/walled garden: Almost all Smalltalk systems basically implement their own operating system complete with their own integrated graphics system/window manager, process scheduler, and so on. It's an amazing environment for creating applications but it doesn't play well with the outside world and there isn't a straightforward way to 'shake' an image down to just your application. Deployment usually comes with the overhead of the entire Smalltalk system and interop with native can be somewhat limited. Imagine if Java applications only ran within Eclipse.

Zipf's law: The popular languages are so popular that their communities generate their own gravity (i.e. lots of effort tends to attract more effort). Despite Smalltalk's many appealing qualities (ergonomics, simplicity, maturity, robustness..) it stands in the shadow of giants; many people don't even know it's there or can't invest the effort to give it a shot so it never achieves critical mass.