It is a matter of skill to a large extent, though. A skilled programmer will write fewer bugs on average than an unskilled one. They'll know the patterns to avoid and have a higher bar for quality. Nobody can write 100% bug-free code, independent of programming language. Also, job title might correlate with skill but it doesn't rule out incompetence at the highest levels.

Sometimes writing shitty code is a result of competence, not incompetence. I've seen much better programmers than I ever will be writing terrible code because it was the fastest way to get a prototype running and find out whether the problem was worth writing good code for.

Writing safer C is a matter of skill.

Writing safe C is a matter of either radically different (much, much slower) process or better tooling or both. Skill is not sufficient.

It doesn't really matter, the most skilled programmers are usually working on harder stuff, so the bug rate remains fairly consistent.

I think it's mostly a testing thing. Valgrind is a friend a lot of people haven't heard of for c/c++. Setting up good regression tests is an art. Maintaining them is even harder.