It's a standard library feature, rather than a language feature.
And you might say, "Who cares? Even freestanding has the standard library". Nope, std::array wasn't added to freestanding. You can dig into the messy details for yourself if you want, but suffice to say your freestanding C++ doesn't have std::array
So the C++ language has "arrays" but they're garbage, and if you point out that the arrays are garbage you're told to use this library feature, which may not be available.
The only valid complaint about std::array is that it's awkward to declare and takes more characters to type. It is, otherwise, vastly superior in every other way.
That doesn't make them garbage. That makes them annoying.
I feel like I already explained it's not even part of the language itself, it's a library feature, you aren't given this feature without the rest of the hosted C++ standard library.
Which is fine if you write Windows desktop apps, but this is an array type, unlike a GUI widget, or an XML parser, it seems like I'd probably want an array type for this $1 per unit micro controller I'm writing firmware for. In Rust the nice array type works just fine, it's a proper first class type, it knows how big it is, mutable arrays coerce into a slice I can sort (only unstably, but hey, we're embedded firmware let's not get fancy), I can iterate over it properly... in C++ only the crappy C-style array is available unless I can butcher the std::array so that it works outside the hosted library. Ugh.
You do not have to butcher. Standalone allocation free implementations are available if you are so in need.
But I see that you bring Rust in here. If that's your cup of tea then use it. No need to spill venom. Personally if I am dealing with $1 micros I very much prefer C with some selected libs for embedded. Do not really have problems with it for such small tasks.
I have never perceived it as a problem. I do not think it really slows my programming. Personally I am the guy who would prefer function() vs fn() but without going into extremes of Java culture. Besides you can always alias it to whatever you want if your fingers are so sensitive.
And you might say, "Who cares? Even freestanding has the standard library". Nope, std::array wasn't added to freestanding. You can dig into the messy details for yourself if you want, but suffice to say your freestanding C++ doesn't have std::array
So the C++ language has "arrays" but they're garbage, and if you point out that the arrays are garbage you're told to use this library feature, which may not be available.