It's extremely important for meaningful commercial Rust adoption for legacy codebases to be able to adopt it incrementally (i.e. all new code is Rust). I think you're underestimating how much C/C++ code there is out there (Linux Kernel, Chrome, all of Google's internal infrastructure, all of Amazon's internal infrastructure etc). We're talking about many billions dollars worth of code that is never going to get rewritten and lines of code that keep accruing. Now competitors starting today may make other choices but there's enormous value to be had by cracking the nut of seamless integration of progressive migration (i.e. so that you can say "no more new C++ code"). The failure of this lesson is seen in banks that continue to run on Fortran at best and at worst other businesses that continue to run on old unsupported languages/technologies. Thankfully, I think the tech companies are engineering-led and understand this so I suspect they're paying people to figure out this problem.
