If you notice, there's some space left between the maximise and close, so they're more like _[]...X Plus, you can maximise/restore by double-clicking the title

If you notice, there's some space left between the maximise and close, so they're more like _[]...X Plus, you can maximise/restore by double-clicking the titlebar which is a larger target and I expect most users learn that and almost never touch the actual button.