Who told you that? You can write entire C libraries and call them from Electron just fine. Browser is a native application after all. All this "native applications" debate boils down to the UI implementation strategy. Maintaining three separate UI stacks (WinUI, SwiftUI, GTK/Qt) is dramatically more expensive and slower to iterate on than a single web-based UI with shared logic
We already have three major OSes, all doing things differently. The browsers, on the other hand, use the same language, same rendering model, same layout system, and same accessibility layer everywhere, which is a massive abstraction win.
You don't casually give up massive abstraction wins just to say "it's native". If "just build it natively" were actually easier, faster, or cheaper at scale, everyone would do just that.
You reduce development effort by a third, it is ok to debate whether a company so big should invest into a better product anyway but it is pretty clear why they are doing this
Part of this (especially the CPU) is teams under-optimizing their Electron apps. See the multi-X speedup examples when they look into it and move hot code to C et al.