You could easily make the same counter argument against including <filesystem> and yet there’s very real value to having something cross platform out of the box that handles elegantly various pitfalls that people typically fall into.
Given that Java followed that path and already acknowledged that mistake by deprecating the original HTTP client, why do people insist in not learning lessons?
What is available as external library has various levels of support quality.
That is why we have POSIX, the C runtime that ISO C didn't want to rely on, yet almost every C program uses a part of it.
Still it was deemed important enough to spend development resources on the POSIX subsystem to make DoD happy, then SFU and now integrate the Linux kernel.
Common sense anyway would suggest that "almost every" is distinct from "many, but also many not", and the latter is what I think would be a better fit here.
The intention behind my comment (and I thought it was clear without any "semantics" discussion required) was to show that there is no need for the POSIX layer to be included as part of ISO C. POSIX is just a "platform layer" (for all I know), meaning that it is much closer to a "library" than a "runtime". I don't see a need to bundle it tightly with the language. Heck, why did I even bring up Windows as a counterexample, when there are probably a lot of more-or-less ISO C conforming compilers for microcontroller platforms that could never support POSIX.
As for HTTP within the standard library, I would probably tend to agree although I’d note that Python does have it in its standard module set and I don’t think there’s an acknowledgement that that’s somehow a mistake. Each language fills a different need so framing it as “people insisting in not learning lessons” isn’t helpful. Not to mention that the best way to learn is to experiment and double check if what was once true remains that way (experts know when and in what way to break rules).