Those projects had to constrained themselves to having 100% of the code available, no binary libraries and lock the compiler versions being used.
Since the early 90's I keep hearing that it is possible to write safe C code, yet outside in the real world, unless constrained by processes like MISRA-C and Frama-C, which isn't really C anymore, it never works.
The proof is the amount of CVE exploits, that get reported almost daily!
Just yesterday while reading some papers on Cyclone, I discovered this jewel:
"X El Capitan v10.11.6 and Security Update 2016-004" release notes
A shame, considering Apple actually has the resources for doing a proper rebase of XNU on L4 and with actual pure microkernel multiserver architecture.
Imply is just slightly too harsh. Writing safe C code is very possible, as proven by projects such as seL4 or engineers such as djb.