It can't do the literal entire thing an operating system is supposed to do: manage applications and their resulting windows, in a sensible way.
I want to know what application is running.
Sure it's in the dock!
I want to find a specific application window.
Go fuck yourself right to hell.
Wait, the taskbar doesn't show the running windows, like it does on every other OS? It's at least discrete right?
It discretely takes up 1.5cm of the bottom of the screen at all times. It's so discrete it doesn't even need to use the corners.
Uh, alright, well that's all the system space you need right?
Yeah of course just that bottom inch or so .... And a top of screen system level menu bar to display what windows does in the bottom corners.
/sigh/ ok, fine, I just want to be able to full screen a window and still see what else is open.
Burn in hell and die.
I want to be able to easily switch left and right between open windows.
Go full screen or I will shoot you.
I want to move an open window into the other monitor.
You can't because you're full screen dumbass.
I want to let a window present a popup like they normally do.
You can't because youre full screen dumbass. Why would you be full screen?
I want an application like Slack to be able to popup and remove notifications when is appropriate.
Choose to have every single notification persists on screen until you manually remove it, or miss all your notifications.
Can't we trouble you for something in between, where we trust an application and let it manage them in a way that makes sense based on their context?
You can trouble me for something in between these cheeks, shit stain.
Like honestly, I fucking hate what an advertising and AI filled mess Windows is, but it can actually manage your windows and virtual desktops in a way that makes a modicum of sense.
It feels like a single Apple product manager decided that the way that they use their computer (a single application at a time, no windows to manage) is the only way anyone does, so who cares if we implement a nonsensical full screen paradigm, it makes one tiny niche edge case slightly simpler.

X closes the window, it doesn't minimize it. The application stays open until you explicitly quit it.
Staying open but hidden is what we call "minimize." "Explicitly quitting" is what should happen when you click the exit button.
In macOS there's the general concept that every window should represent a document. You can have several documents open, such as PDF files, web pages, Word documents, etc. For a running application, you can have zero or more documents open at the same time, meaning you can close all documents and still have the application open.
🤷♂️
If I close all documents I don't want the app running. It takes up visual space in the dock making it more cluttered and it takes up more RAM or swap space that I'd rather have allocated to things I'm doing than to things I've told the computer I'm not doing.
Understandable, but it's just not how macOS works; it's an intentional paradigm. I guess the use case is "dealing with documents", opening, editing, closing, in repetition.
But closing the application and all its open documents in one go also has a common UX pattern: Command+Q. So if that's what you really want, do that instead of closing windows/documents.
It's just a very simple matter of making happen what you want to happen instead of not doing that. 🤷♂️
With all this said, I don't think macOS is a good operating system. It's very well thought out and very cohesive and very nice looking, great for beginners. But it's just not practical for me. The window management is clumsy and lacks a lot of features, I don't like how applications are installed (or uninstalled; sometimes packages can't be easily uninstalled), and I don't like how the hardware will just not support the latest operating system after a while.
With Linux, I can just keep going and upgrade the system in perpetuity and it'll just keep going.
I also find tiling managers are good, but after about 15 years with i3 I've committed myself to Niri. It's so good. A whole new paradigm that fits my mental model very well.
That makes absolutely no sense at all.
Why not? Sounds reasonable to some extent.