This behavior is intentional. You are probably used to working with programs that have a workspace that expands with the document, such as a word processor, spreadsheet, Internet browser, or e-mail program. First Class has defined elements that take up a certain amount of room, such as you might find with (for example) your anti-virus program, or the game of Hearts (which can't be maximized either). If you were able to maximize First Class, it would look something like the graphic below. As you can see, there really is no reason to maximize First Class.