The C juggernaut illustrated
Perhaps it is tempting, looking back at history from the vantage point of today, to say that C succeeded so much because it was at the right place at the right time. As you could tell the story, all sorts of people in the 1980s wanted a low level programming language, C was around, and so they seized on it. Any similar language would have done; it's just that C was lucky enough to be the one that came out on top, partly because of network effects.
(This story is especially tempting to people who don't like C and Unix.)
This significantly understates the real appeal of C at the time, even and especially to people who had alternative languages. A great illustration of this is C on the early Macintosh. You see, unlike environments like MS-DOS (which had no language associated with it, just assembler), the early Macintosh systems already had a programming language; they were designed to be programmed in Pascal (and the Mac ROMs were originally written in Pascal before being converted to assembler).
This was more than just an issue of Apple's suggested language being Pascal instead of C. The entire Mac API was designed around Pascal calling conventions and various Pascal data structures; it really was a Pascal API. Programming a Mac in C involved basically swimming upstream against this API, full of dealing with things like non-C strings (if I remember right, Mac ROM strings were one byte length plus data). I believe that Mac C compilers had to introduce a special way of declaring that a C function should have the Pascal calling convention so that it could be used as a callback function.
Despite all of this, C crushed Pascal to become by far the dominant programming language on the Macintosh. I don't think it even took all that long. Programmers didn't care that dealing with the API issues were a pain; working in C was worth it to them. It didn't matter that Pascal was the natural language to write Mac programs in or that it was a perfectly good language in its own right. C was enough better to displace Pascal in a hostile environment.
C did not win just because it was at the right place at the right time. C won in significant part because it was (and is) a genuinely good language for the job it does. As a result it was the language that a lot of pragmatic people picked if you gave them anything like a choice.