[RealityVoid]

That's the thing, you have layers upon layers of stuff that run on the computer. You have a runtime of the language, many many abstractions of interacting with the various capability of the system, a ABI to the OS, an ISA. These things vary and you need to account somehow for these variation. And the changes in the lowest layers percolate through.

Not to mention that the computer is actually very very different than what you imagine.

I say this not to make excuses for react, again I don't know that ecosystem. I spend most of my time writing firmware and low level drivers. And I see during my work the wide array of capabilities and approaches these systems have. They are not an homogeneous bunch.