I think he was thinking about the many modern programming languages which essentially cannot be implemented without a thick runtime (garbage collection, run-time compilation...).
Such a runtime allows programming languages to be much easier to use in common application development use cases, but it is also a large price to pay in terms of memory requirements, achievable performance, and predictability. This is why languages which such runtime requirements are typically not used in scenarios such as low-level OS layers or foundational numeric libraries.