Most of us use C and assembler for low-level tasks, even if we can use high-level or multi-paradigm languages just as well to accomplish them (for example, you can make an assembler in Lisp using macros (or you could make one in Forth), and just use the FFI to run the code directly, like it was natively generated). In general, C is useful to have, but it's not a requirement. Most garbage collectors are still written in C as it's a low-level memory management problem and tends to require access to various non-portable OS APIs. Rest assured that this could be done entirely without C (but not without the platform's assembly and knowledge of the ABI), however C's purpose is such things and most people just use the right tool for the job!
As for SEPPLES, the only time I have to touch it is when I'm reading or editing other people's code.