Than UNIX fork/exec model, or calling into Create Process all the time.

Windows has a more rich set of IPC stuff than POSIX, especially since it has a microkernel like design.

If you are going to say it is everything on the same memory space anyway, it isn't.

Optional on Windows 10, and enforced on Windows 11, Hyper-V is always running, and several components including kernel and driver modules are sandboxed into their little worlds.

Several additional sandboxing changes were announced at BUILD.