There's also an ergonomics to process creation APIs - rather than needing separate APIs for manipulating your child process vs manipulating your own process, fo

There's also an ergonomics to process creation APIs - rather than needing separate APIs for manipulating your child process vs manipulating your own process, fork() lets you use one to implement the other: fork(), configure the resulting process, then exec(). CreateProcess* on Windows is a relative monstrosity of complexity compared to fork/exec.