Maximized windows cover up the entire desktop. Since there is no minimize command here (TOS is still heavily single-tasking), it would be incredibly difficult to open up a new drive or cartridge.
You can now also see that files are being displayed as text instead of icons. The icons in TOS aren't really graphical or sophisticated anyways so there isn't much of a difference.

As you can see, the trash can still can't be displayed in a window.

The preferences aren't really any more advanced than GEM for DOS, but here we are running in Medium resolution (640*200), which is why everything appears squished. The Atari TT's resolutions are much larger than this.

For those wondering, this is what High resolution (640*400) mode looks like. It was only available on a special monochrome monitor.