Question

Why is it relatively rare to observe a solar eclipse

Answer 1

Because the planets have to be aligned just right for it to happen

Answer 2

If the moon's orbit was a perfect circle, then there would be at least one solar eclipse every month. As it is, the moon's orbit is not a perfect circle, so usually it is too far away from the Earth to block the sun out completely. Only about 3 solar eclipses happen every year.