The problem is that if you don't maximize everything, you'll wind-up with a series of windows which overlap in a less than useful fashion - menus, scrollbars and headlines get obscured and you need to mouse-around-the-screen to do anything.
There are dual problems here. Window Managers are designed to give a "comforting intuitive interface" rather than an interface which lets you do things quickly. But also, manufacturers pump out wide screens intended for video viewing rather than long screens which are suited for text viewing. This also means a good portion of web pages use fixed-width pages to keep from being stretched to unreadability. But these also keep the text from being read from a narrow screen (sure, they could set a max width with CSS but fixed-width also lets the designer guarantee their design looks exactly as they wish).
There are dual problems here. Window Managers are designed to give a "comforting intuitive interface" rather than an interface which lets you do things quickly. But also, manufacturers pump out wide screens intended for video viewing rather than long screens which are suited for text viewing. This also means a good portion of web pages use fixed-width pages to keep from being stretched to unreadability. But these also keep the text from being read from a narrow screen (sure, they could set a max width with CSS but fixed-width also lets the designer guarantee their design looks exactly as they wish).