The OS won due to a number of factors. The language came with it. Then, as the OS spread, the compilers for its source language spread. Then that language was everywhere. With that OS and language everywhere, esp on cheap machines, ecosystem effect kicks in from there where people start building on, using, or targeting it. Most portable and fast language isn't why it succeeded as UNIX could've been built with alternatives. UNIX itself was the killer app that caused C to flourish.