Algorithms are now more efficient at keeping a processor occupied than hand tweaking, with the complexity of processors being what they are, w/ multiple instruction pipelines and vector processing, multiprocessors and such. C is the equivalent of what ASM used to be. It is the least complicated abstraction language that a processor manufacturer can provide low level developers. Many processors are built with the language in mind. As a result if you want to extract the most performance from your hardware, C is the solution. Many higher level languages are written in C, or the core components that HAVE TO BE fast are written in low-level C.
C is also "almost" portable. Which generally speaking means it can be used across families of processors with greater efficiency, while maintaining performance.
Also there's still a hellalotta stuff, core libraries, drivers, embedded software, and software frameworks written in it... so yeah, it's not going away... I use it daily.