Parsing text is always expensive on the CPU, that's why it's better to often prefer binary files when it's possible.
It's also the reason the DOM is so slow, in my view.
I remember spotting a lot of fast JSON parsers around, but again, there doesn't seem to be any popular, open, flexible, binary file format out there.
Meanwhile, games are always larger and larger, machine learning requires more and more data.
There is ALWAYS money, battery and silicon to be saved by improving performance.