Which is annoying for some applications which don't maximise, because the content isn't there but could be. I can't think off what does this off the top of my head since I installed Amethyst, but I think I remember Excel used to do this back in the day.

I hate the thought behind this. Often I don't maximize to see more content, but to hide everything else. Why does Safari decide for me that the window can't be any wider? That doesn't make any sense at all.

Note that this concept predates the concept of maximisation, and comes from an era when single apps would be implemented in multiple windows. E.g. the content area the toolbar in photoshop were separate windows. Back then it made a lot of sense. But I agree it's just annoying now.

If you want such maximisation (and not fullscreen as was described), you can use apps like Moom or Magnet.

That this functionality is not builtin is the most baffling MacOS design choice I have ever seen.

We can split hairs and hold our breath til we're blue discussing design decisions we don't control.

I'm just trying to be helpful, possibly barely pointing out that things claimed to be impossible are not (and not argumentatively, only because folks may stop at that and have to endure something when there are solutions that would fit their use case)