[Someone]

On the original Mac, you had to hold the mouse button down while making a menu item selection.

I am not sure why they didn’t do what Windows later did, and allow users to open the menu with a click, and select an item with a second click, but it might be as simple as that the thought hadn’t crossed their mind.

[hugi]

As a user that started my GUI life on an older Mac, hold-release menus always felt intuitive and "sticky menus" really felt weird when I first encountered them.

The logic behind that initial design was that menus were really just "buttons with options" and a mouseup should initiate an action. The menus had few items so there wasn't much dragging involved.

As software evolved, menus grew and spending an entire click on "present me with your selection of options" just became sensible.