Comment by moron4hire

I think it's easier to understand if you consider the opposite case: how could the moon never be on the Sun-Earth ray? It would have to orbit Earth around the Sun-Earth ray. But the Sun-Earth ray changes direction as Earth orbits the sun, so the Moon's orbit would have to change with it. People in the northern hemisphere would not be able to see the moon at the same time as people in the southern hemisphere for significant portions of the Lunar cycle, and we would always see a half-moon.

That the Earth-Moon orbital axis is not incidental with the Sun-Earth orbital ray means we'd always, eventually, have solar and lunar eclipses.

Perhaps if Earth were in a tidally locked orbit with the Sun, the Moon could be in a tidally locked orbit with the Sun while also orbiting the Earth. But then half the planet would be frozen and the other half would be completely baked and we wouldn't be having this conversation.