This is not unusual at all. Windows allowed it for years before Linux came along. It was also true of some other *nix systems - IIRC, Ultrix (DEC) allowed this, and so did Dynix (Sequent).
*BSD allows it too, or used as of 2022.
What is unusual about Linux is that it guarantees a syscall ABI, meaning that if you follow it, you can make a system call "portably" across "any" version of Linux.
Sure, I’m speaking about platforms that are relevant today, not historical ones. Windows, MacOS, {Free,Open,Net}BSD, Solaris, illumos, none of these do.
It's quite easy to find out the actual situation on this since Go decided to do it their way. Last I checked, OpenBSD is the only OS where they go through libc, but I haven't really kept up.
