The null-terminated string is the most compact memory representation for a string. A strong competitor was Pascal strings which are led with a byte that carries

The null-terminated string is the most compact memory representation for a string. A strong competitor was Pascal strings which are led with a byte that carries the length of the string. The only problem is that limits you to 255 characters in a string. You would have to do some UTF-8 style length encoding to make it memory efficient while still capturing long strings. Older computers had a lot less memory. Programs would write their own virtual memory systems to swap code and data to and from disk. C was born in this era. By the time large flat memory and many registers were available, the old C string was already the standard. It is very difficult to get away from that because everything from the OS on up assume standard C strings.