Unix and C were written in an agile fashion. C was a step up from a macro assembler, to be used for writing an operating system. String manipulation is rare in operating systems, certainly in those days (even if you felt a need, you don't have much room to create new strings in if your system and its applications must run in 64 kilobytes of RAM (144 kB for the PDP 11/45; see http://cva.stanford.edu/classes/cs99s/papers/ritchie-thompso...)

The filesystem was about the only place where strings got manipulated and there, filenames were stored in fixed-size (14 bytes) buffers. Since all code could know strings were at most 14 bytes, having a complex type (pointer,length) was deemed a waste of memory and performance there. Everything else followed from that.

It would have made C a profoundly different language. C is what it is; a portable assembler. I believe K&R had a strong sense of minimalism; fancier string s would be seen as something that belonged in a library not the language.

This has its benefits; _anything_ fancier would have embedded a whole set of assumptions about typical string handling usage for which the design had optimised.

That no safer string handling library became popular can be seen as a indictment of C or a tribute to their tasteful restraint.