What is a primary reason an increase in glaciers on land would cause sea level to fall? g?

The amount of water on the planet is fixed; it neither increases or decreases. Glaciers are sheets of moving ice. This water to form these extensive sheets must come from somewhere. The water comes from the most extensive store on the planet; the oceans. Ice Ages always corresponds to periods of low sea level because much of the ocean water is is land locked as glaciers.