This way it becomes easy to memorize key sequences; start by navigating with arrow keys, then eventually speed up as you memorize each menu item's mnemonic key, and if you ever forget, just look at the menu.
It was the keyboard-friendliest idea ever, without requiring any sort of terminal. I'd even say friendlier than MacOS (heresy!!) or, yes, VIM (burn the witch!!!)
So even if the developer forgot to configure mnemonics, which was as easy as prefixing a letter with ampersand, you could navigate by keyboard. Sometimes tedious but beats not being able.
> I'd even say friendlier than MacOS (heresy!!)
Honestly, I disagree. If you've used macOS for a length of time, you might be aware of the universal menu search system using (cmd+? i.e. cmd+shift+/). Hit that, type the menu item name, and simply hit return to activate it. Doesn't get simpler than that. The alt+ system always feels very janky to me on Windows because on many apps, hitting Alt relayouts the entire app sometimes to show the menu bar on top.