It's a fair point. I think loss-aversion over React (Native) is to blame.
Their current client stack is:
Web: React
Desktop: React + Electron
Mobile: React Native + Native
Their commitment to React on so many platforms makes it easy to accumulate bloat. Their need to support lower-level features means they can't avoid native code altogether.
I wonder why they stick with it.
My guess is they don't want to add more hires just for this problem