> I couldn't tell you exactly why (though I have some ideas), but Lisps seem to settle into amazingly stable languages. Even Clojure, with all its initial trendiness, has been remarkably resistant to bloat and churn.

I would say that the core reasons are well understood:

1) The fact that there is built-in syntactical stability in any Lisp since the code must comprise valid Lisp data structures + a couple of special symbols.

2) The second reason has to do with the fact that Lisp macros allow language extensions directly by users, provided those extensions comply with fact 1. When users can extend the programming language by adding libraries, there is little reason for the programming language designers to chase every trend in language design, ending up with the kitchen sink—sorry "multi-paradigm"—languages of today. The core stays small.