Patches are reviewed just not in the way you are accustomed to, but it doesn't make it any less secure. The kernel is continually audited and tested, and is the most widely used kernel in security devices.

What you are asking for is that developers should have to prove their real-life identity and authenticate to a public SCM system and that somehow makes it more secure, when hidden exploits could as easily be sent as a PR on GitHub and merged by someone who didn't know better or who can just play dumb.