That entirely pragmatic reason was to be assembler with curly braces. See memory capacity of PDP-7 and think what you can reasonably compile with those resource

That entirely pragmatic reason was to be assembler with curly braces. See memory capacity of PDP-7 and think what you can reasonably compile with those resources. Fun fact: if you don't specify variable's type, modern C compiler assumes int, this is how the first C compiler worked, you don't need types in assembler, the register type (machine word) is almost the only type you deal with. Implicit function declaration is an assembler feature too.