What if they are phases of evolution? A small team that can speak a lightweight language can quickly change velocity (speed and direction), iterating until a PoC is a useful system. Once the interfaces and the protocols fall into place, calcify or harden the design by converting to something more static, more literal.

Imagine going from something like lisp to Ada? Or lisp to Rust? Write quick prototypes in lisp, solve the hard problems of understanding the domain, then convert portions that require correctness to a language that is amenable to correctness checking (property testing, model checking, etc).

I think gradual typing [0] (not Gradual Typing) or language embedding [1] are steps in that direction. In a way, lisp can be thought of as a CASE tool for bootstrapping new systems.

The great thing about language platforms (JVM, Beam, Graal, Wasm, Racket) is that many languages can easily exist in the same system so that in many cases, code can be converted on a function by function basis.

[0] http://mypy-lang.org

[1] http://terralang.org

The SW world is full of Java/C++ rewrites of products that originally started out in a dynamic & productive language like Lisp or Python. It might make sense in the lifecycle phase when you're past making big changes under make-or-break pressure, and are in the "provide predictable 10 year maintainance roadmap for this large codebaes" stage. You end up employing different kinds of programmers too because many of the original team may be reassigned to something more exciting/important to do.

But it's in no way inevitable, of course, there are many old Lisp, Python, etc codebases in production too.

BTW. I've been trying to rediscover this blog post and can't seem to find it again, anyone? It described different kinds of software projects, the (1) kind that try to deliver incremental improvements (eg 10% cost savings), and the (2) kind that try to make 10x improvements, and the difference in how those projects are run (the 1-type project can't go over budget because it will then deliver negative value etc).