Why would we move on? C is a local maximum, like a Brayton-cycle gas turbine engine. A 787 engine is no more than 50% more efficient than a 707 engine, despite tens of billions of dollars in investment and decades of R&D between the two. And we won't get even another 50% improvement any time soon. It'll take a fundamental change in technology to move past that plateau.

C is likewise on a plateau. There is nothing categorically better than C for what C does; just different points in the design space that make different trade offs. E.g. Rust gives you memory safety through ownership, but you can't even make a doubly-linked list while staying within the ownership system. In a different point in the design space, Go has garbage collection, but that comes with its own trade offs. All of these might become obsolete when we have e.g. quantum computers. But in the meantime we are just playing with different trade offs, because we've captured all the low-hanging fruit decades ago.