The point is that even if all code commits are scanned as safe by ai, black hats can still analyse the commits and diffs to find vulnerabilites for people who havent patched yet.
Scanning every commit doesnt automatically make everyone in the world patch immediately, vulns can still be found from commits and diffs and used against those who havent patched yet.
Look at GP to my comment again, the one I was clarifying: they're not talking about black hats or any other kind of hacker, they're talking about the original developers and preventing such vulnerabilities from existing in the first place.