Have you ever used a Mac Extreme Coder? There is essentially no way to maximize a Window to fit across the entire screen. The maximize button, instead, serves to set the Window at the width necessary to display all the content in the Window (a webpage like this appears to be about 600 pixels, maybe more, I don't know as well on my laptop), and then the necessary vertical (often, the whole screen, but sometimes not).

It's unique to MacOS and has been for quite sometime.