Earlier quoted context omitted.
That's because it's not Maximize, it's Zoom, which uses content hints to resize the window while not wasting space with useless empty space inside the window, thus still allowing one to see other windows. When there's no content size hint it falls back to what Windows and Linux call Maximize, which is more like a windowed fullscreen mode.
This probably reflects my not 'coming from' macOS or idiomatic ways of working in it, but I basically never hit 'maximize' on a window because I want to see more of whatever happens to be in the window. I hit 'maximize' because I want to use an app's internal features (tabs, split panes) to manage multiple app-specific contents/views instead of external window management. I'm never like > Ah, just let me resize my br…
Now, in practice, Zoom is really nice when it works (I'm using it all the time with Finder+ windows), the problem is that it takes a single app not providing the content size hint for it to break and make it confusing. And then a vicious circle starts where more apps don't care about what it's supposed to do, and before you know it Zoom is mostly falling back to being Maximize most of the time, and people wonder why when it's doing the original Zoom thing it behaves differently and think it's weird and broken (which is perfectly understandable)
In a way Apple either did not embrace the winlin paradigm enough (e.g having a proper Maximize alongside Zoom + having an option for per window cmd tab) or they did not stick to their guns enough (enforcing Zoom to be correct + having a worthy fullscreen/tiling implementation) and we're left with a shitty compromise.
+ A very similar case that ties into this is how the Finder went from being fully spatial to a half-spatial half-global compromise.