Because everybody can draw their own menu in their window. Like Sublime and VSCode do. Nevertheless, if you require that, why not make the place where the menu

Because everybody can draw their own menu in their window. Like Sublime and VSCode do. Nevertheless, if you require that, why not make the place where the menu is displayed configurable? KDE does - it offers 3 options: the global Mac-style menu (which you can put anywhere, even in the middle of the screen if you want), classic Windows-style menus or "hamburger" menu buttons (utterly inconvenient but I'm still glad there is an option for those who like it).