Yes, annex k was generally judged to not be very helpful in practice[0]. However, I agree that it might make more sense as a component of an environment that mandates strict static analysis and code review. (Microsoft also has other extensions with similar roles, e.g. their in and out parameters.) In that context, it makes perfect sense: microsoft wanted to upstream some components of their static analysis pipeline, but those components ended up being useless without the rest of the pipeline.

0. http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1967.htm