Why can't I see the moon at night sometimes?

Because the moon is basically on the same side as the sun in the sky these days, it can't be seen at night.

It's the end of June in the lunar calendar, and the moon phase is between the last quarter and the waning moon. It rises from the east every morning, and it is a big crescent moon. Soon after the sun rose, the sky brightened and the moon was almost out of sight.

At night, the moon will set before sunset, so you can't see the moon at night.

The moon these days is like the one in the lower right corner of the picture below.

Moon phase diagram