Look carefully at the diagram, please, and notice the rounded tip at the bottom (right side in the diagram). That is one contact of the bulb. The threads where the wire is attached form the second contact. As the others have said, in this diagram the + side of the battery is connected to the - side by the wire, resulting in MAXIMUM current!
In order for the bulb to light up there must be current passing through one contact, through the filament, and through the other contact. That's what we call a "complete circuit". In the diagram with the one contact not connected it's what's called "open circuit", so, no light.