Because the position of the moon, earth, and sun are not in the same exact place every month. This means they are a rare occurrence and only happen when the moon, earth and sun are in exact alignment with the earth.
Solar and lunar eclipses don't occur every month because the orbits of the Earth and the Moon are tilted relative to each other. Eclipses can only happen when the Sun, Earth, and Moon align perfectly, which occurs during specific phases of the Moon (new and full). This alignment happens only a few times a year, resulting in a limited number of eclipses rather than one every month.
A lunar eclipse can occur multiple times a year, but the frequency can vary. On average, there are about two to four lunar eclipses each year. Lunar eclipses can be partial, total, or penumbral, with total eclipses being less common.
Because the moon phase is irregular
There are two main types of eclipses: solar and lunar. Lunar eclipses occur every 6 months. Solar eclipses occur 2-5 times per year. Eclipses can be partial or total. Partial eclipse covers only part of the sun or moon, while total covers the full entity.
The Earth orbits the Sun in a plane that we call the "ecliptic". If the Moon orbited the Earth in that same plane, we would experience eclipses every month. But the plane of the Moon's orbit is about 5 degrees tilted from the ecliptic, and so we only see eclipses at the "nodes" when the Moon's orbital plane crosses the ecliptic at the new or full moons.
The moon would have to be on a flat plane instead of being on a tilt.
We do. its not a month though. its every 29.5 days
Every year
Eclipses don't happen every month because the Moon's orbit around Earth is tilted, so it doesn't always line up perfectly with the Sun and Earth. This alignment is necessary for an eclipse to occur.
A lunar eclipse can occur multiple times a year, but the frequency can vary. On average, there are about two to four lunar eclipses each year. Lunar eclipses can be partial, total, or penumbral, with total eclipses being less common.
Because the moon phase is irregular
There are two main types of eclipses: solar and lunar. Lunar eclipses occur every 6 months. Solar eclipses occur 2-5 times per year. Eclipses can be partial or total. Partial eclipse covers only part of the sun or moon, while total covers the full entity.
The Earth orbits the Sun in a plane that we call the "ecliptic". If the Moon orbited the Earth in that same plane, we would experience eclipses every month. But the plane of the Moon's orbit is about 5 degrees tilted from the ecliptic, and so we only see eclipses at the "nodes" when the Moon's orbital plane crosses the ecliptic at the new or full moons.
The Moon's orbit is at an angle to the orbit of the Earth around the Sun so most often the full/new moon is 'above' or 'below' the line directly from the Sun to the Earth so lunar/solar eclipses do not occur every month.
The moon phases would change.
Typically, lunar eclipses occur once or twice a year. Because more than half of all lunar eclipses are partial, and because lunar eclipses are visible only from the side of the Earth where the Moon is up, you would generally be able to see a total lunar eclipse every other year or every 3rd year from your location. The rest of the eclipses would be either partial, or not visible from your location. You can check the NASA Eclipse Web Page to see the catalog of all eclipses from 2000 BCE to 3000 AD at the link below.
Every month, dummy!