Do you have a tiny monitor? I find that people with small mointors maximize their windows because they have to.
I have a 27" widescreen. The idea of maximizing a browser window is absurdity. My monitor can comfortably show three websites side by side. The amount of wasted white space on a full screen website would approach 90%.
Here's this very post fullscreened (without a taskbar). What a wild waste of space and the content is clearly not designed to be viewed like this, with the UX being located at the top left lol.
https://i.imgur.com/NPxks8b.png