Why don't lunar eclipses happen every month?

Why don't lunar eclipses happen every month?

 

The Moon's orbit is at an angle of 5.1° to the Earth's orbit. This is not much, but is sufficient to ensure that the Moon can travel up to 37 000 km above or below the centre of the Earth's shadow. A lunar eclipse is only possible when the full Moon crosses the Earth's orbit, and this only happens twice a year. Unlike solar eclipses, which can only be seen by observers watching from small portions of the Earth's surface, a lunar eclipse can be seen from anywhere on the side of Earth facing the Moon.