In practice, C++ and Python codebases have insane amounts of churn. They're constantly moving targets and require a lot of overhead to keep in shape, from just about every perspective: performance, security, maintainability, implementation compatibility, etc. It's tolerated though because it's standard practice, and we developers get a paycheck anyway.
Languages like OCaml, Common Lisp, Haskell, and other niche but obviously practical languages continue to be indispensable to certain cohorts of companies and developers. While I do agree that Lisp specifically peaked in popularity decades ago, it still exists in the commercial domain with resounding staying power, even in environments where it could in theory be replaced by C++ or Python.
It's also abundantly clear there's a hunger for new (or at least replacement) languages for the stalwarts. Rust, Julia, Mojo, Swift, and OCaml are a few such languages that get attention in their commercial investment and development, often with the specific purpose of replacing Python or C++.
As a personal anecdote, I find professional Common Lisp programmers generally to be quite sensitive to matters of bloat. Some programmers go as far to chisel away needless cons cells (or allocation in general), and constantly be in touch with the compiled assembly—something frequently ignored by professional C++ programmers of comparable experience.
I would love to hear the "very sound technical reasons" explaining Common Lisp's obscurity. Given the vast and diverse biome of programming languages in use today, including and especially in professional settings, I'm quite interested in understanding what technical reasons uniquely relegate Lisp to obscurity.