A large number of people know how to write C, C compilers are very mature and ubiquitous, C libraries are very mature, portable C code isn't difficult to write,

A large number of people know how to write C, C compilers are very mature and ubiquitous, C libraries are very mature, portable C code isn't difficult to write, C is good for constrained environments like embedded, for writing drivers, for interfacing with OS routines, etc.