Spicy hot take: the root cause here is the awful c++ library ecosystem.
Yeah no. While the C++ library ecosystem is painful to use, it still doesn't justify hand-rolling a JSON parser and there are certainly high quality hash-based container implementations available too, but even the standard one should beat the one used here.
But there is no "standard one"...reaffirming the point that you disagreed with. C++ standard library is blatantly missing key pieces given how long the language been around.