There is an accident of history here. Go was developed with the plan 9 C compiler suite as a starting point. Most notably those compilers did not generate assembler -- they emitted object code directly. This is described here: https://9p.io/sys/doc/compiler.html. The assembler facilitated transforming hand-written assembly to object code. And here the plan 9 folks chose a new syntax, probably because it was simpler to start afresh over using the existing "AT&T" or "Intel" syntax.