The real issue here is that the hardware isn't capable of sandboxing without introducing tons of side channel attacks. Lots of applications are willing to sacrifice a lot of performance in order to gain the distribution advantages from a safe, sandboxed execution environment.
This is the real issue. The other comments here are talking about dev-productivity, but they have the causal chain backwards. The browser overhead is about running in a sandbox, on arbitrary/unknown hardware. Web development had poorer DX than desktop app development for a long time, until the critical mass of web-devs (driven by the distribution advantages) finally drove the DX investment to heavier on the web side.
