People use C for writing embedded operating system kernels and other
components such as device drivers because it's a boneheadedly simple
technology for doing so that someone with an EE degree can understand.
On the other hand, these systems written in C exhibit bugs that
require years to hunt down, not to mention laughable security holes
that are discovered years after initial deployment. So it's hard to
conclude that C is actually a successful tool in its domain of
application. But when it's not corrupting data, or sending a copy of
it to an intruder's machine, and when it's carefully written to avoid
doing stupid things like copying the same data many times between
layers of code, code written in C can run fast as hell!