It has to do with the orbit of the moon. The moon orbits on a tilt, so when it’s behind the Earth, it’s not caught in Earth’s shadow, except during a Lunar Eclipse. During which, you can actually see the shape of the earth as the shadow slowly covers it.

Because of the tilt of the moon’s orbit, the full moon is actually higher up during the winter than the summer. In the above picture, the Full Moon is quite high up, but, if the sun were to be on the other side, the moon on the left would be the New Moon so we wouldn’t see it, while the moon on the right would be the Full Moon, and would now be much lower. In perfect, ying-yang fashion, the Sun is highest in the summer.

(photo horrendously not to scale)

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