Well I mean, recently because they have no idea how to make good UIs, and have not read their own enormously detailed (and excellent) Human Interface Guidelines tomes from 10, 20, and probably 30 years go, and have basically regressed to barbarism.

But before that relatively recent fall-off-a-cliff event (whatever it was that caused it, most of us will never know), it was pretty clear that they didn't want to implicitly endorse the lazy/anti-user/Windows-equivalent-UX antipattern of having apps that intentionally made themselves accessible only from a menu bar icon.

I hate the App Store shite that goes wildly too far the other way, but I don't quite understand wwhy they couldn't figure out a way to enable the menu bar widget API in a way that failed if your app didn't also have a way to open via all the normal ways (double-clicking the icon in /Applications, asking Siri to launch it, etc)