When you drop the semantic silliness of C++, like having the container to take care of constructing, copying, moving, and destructing, not to mention exception safety, a basic implementation of a "templated" dynamic array implementation in C comes down to like 100 lines. Hash map will be a bit more, and is not so trivial to write.
It's true that there should be no need to write these things yourself. The alternative C++ gives is not really tempting. A language designed for demanding game development doesn't exist (yet), so one evaluates which is the least worse option.
Considering that vector, map, etc are widely used and expected features of software development, I would think that good libraries in C exist for these already, so you don't have to even write your own 100 lines. Are there any?
GLib (not to be confused with glibc) from the GNOME project has a wide range of functionality -- generic lists, hash tables, strings etc.: https://en.m.wikipedia.org/wiki/GLib
Qt, I believe, also comes with a bunch of "standard library" stuff unrelated to UIs.
Yes, GLib basically implements its own full-fledged OOP system on top of C. At which point, you start asking yourself, why are you not using C++?
In my experience, most of the people who say they don't need OOP or generics end up implementing a limited (or even a full-fledged) version of these things themselves.
Hashmaps to the side ( that's more challenging in 'C' and one really compelling feature of C++ ) the rest can frequently be "faked" with arrays. Obviously, scale matters - having fifteen "vector" implementations in a given system means a little bit of library-ness is in order.
Much also depend on how much you really need dynamic allocation - it can be optional.
This is one of the reasons why every time I get nostalgic about C I then immediately get depressed. Having to find the next level of functionality, libraries, all over the internet, just makes my brain turn to peanut butter.
I think this is one of the biggest disadvantage of a mostly standards based, no particular organization in charge type of language like C, as opposed to, say, python.
I am fortunate that, at the moment, my needs are mostly casual and very rarely performance focused. If I needed C I would just STFU and use C, accumulating my own workarounds for the dispersed nature of its resources.
It's true that there should be no need to write these things yourself. The alternative C++ gives is not really tempting. A language designed for demanding game development doesn't exist (yet), so one evaluates which is the least worse option.