Comment by JdeBP

I really should write that "Yes, Virginia; executables once went in /etc." Frequently Given Answer.

Because it was /etc (and of course the root directory) where the files for system boot and system administration went in some of the Unices of yesteryear. In AT&T Unix System 5 Release 3, for example, /etc was the location of /etc/init, /etc/telinit, and /etc/login .

sbin is actually quite complex, historically, because there were a whole lot of other directories as well.

* https://jdebp.uk/FGA/unix-path-and-personalities.html