Actually, the reason was more that C was designed for systems programming, and that sort of code often has to interface with hardware devices through memory-mapped registers. To do this, you need to be able to write code that uses variables of the correct width. This is why C has all the various sized variables in signed and unsigned variants.
Good point -- C was designed to interface with hardware ("high level assembly") whereas javascript was designed to interface with web pages & browsers. Either way, the history helps understand the design decisions.
For example, why does C have a separate short and long data types, but javascript just has "var"? Because when C was made, memory was at a premium. When javascript was invented, everything could be a 4-byte value.