It would still be worthwhile to greatly reduce the number of vulnerabilities coming out of new C and C++ code, which are likely to be with us for a long time still. At the very least as updates/fixes to existing codebases.
Yes, no doubt - reducing the number of vulnerabilities is a good thing. What I'm worried about is that they merely reduce the number of CVEs, and call it a win for their safety initiative. It becomes a PR exercise more than technological improvement.
But Microsoft (for instance) certainly has incentives to avoid being the next Boeing or Volkswagen with respect to being excellent box checkers that end up missing the mark on the outcomes those checkboxes are supposed to protect against. It doesn't matter if C and C++ have fewer CVEs as such if Microsoft tools and platforms gain a reputation as being insecure or unsafe.