it's a (then-)safe default from the age when having 1GB of RAM and 2GB of swap was the norm: https://linux-kernel.vger.kernel.narkive.com/U64kKQbW/should...

Probably a safe default as there's extra memory of kernel structures, file buffering, SSH sessions to allow logins to debug why your server suddenly has high load and high IOwait (swapping).

If you know a a system is going to run (e.g.) a Postgres database, then tweaking the vm.* sysctl values is part of the tuning process.