Hukked Millet (A whole grain) - Why millet must be hulled before being used as food?

Why millet must be hulled before being used as food?

The following info has been extracted from

http://wholegrainscouncil.org/whole-grains-101/millet-and-teff-november-grains-of-the-month

Today, millet is the world’s sixth most important grain. India is the world’s largest producer of millet, with eight African countries and China making up the rest of the top ten producers. Depending on variety, millet can grow anywhere from one to 15 feet tall, and usually have a very hard, indigestible hull that must be removed before the grain can be eaten. Most millets do best in dry, warm climates.

Note: So Hulled Millet is a whole grain!