That was deliberate. Works on Linux and Windows as well. I think this is the current RFC: https://datatracker.ietf.org/doc/html/rfc5735

You can do:

python3 -m http.server -b 127.0.0.1 8080

python3 -m http.server -b 127.0.0.2 8080

python3 -m http.server -b 127.0.0.3 8080

and all will be available.

Private network ranges don't really have the same purpose, they can be routed, you have to always consider conflicts and so on. But here with 127/8 you are in your own world and you don't worry about anything. You can also do tests where you need to expose more than 65k ports :)

You have to also remember these are things established likely before even DNS was a thing, IP space was considered so big that anyone could have a huge chunk of it, and it was mostly managed manually.