It likely has exactly the same layout because sometime, long ago, some program (e.g. Adobe Type Manager) extended that UI, either by patching its code or by overlaying part of the window with frameless windows containing new controls.

Backwards compatibility doesn’t only apply to APIs.

It also got used less and less. You had to really try hard to install fonts that way and why bother changing something that (a) works, and (b) only a tiny fraction of your users are ever going to see.

Adding a font no longer uses that dialog. It was fun though - an Easter egg in the time beyond Easter eggs.