C inherently does spend more CPU time on memory management than some GC systems.
The fact that a lot of C/C++ fans do not properly profile those areas of their programs does not mean they do not pay for them.
Or that defensive coding (assuming they do not want to introduce a happy little accident of CVE into the world) is free compared to having compiler lift necessary asserts outside of hot loop.
Some memory-safe languages even provide a faster feedback loop on exact instructions that will be executed for all code you write (probably most famous example is Common Lisp, which mandates that DISASSEMBLE is accessible to developer at all times)