Why shark always lost its teeth?

Teeth of shark was demand while hunting.
New teeth will replace them.

The teeth of sharks are not attached to the jaw, but iframeded in the flesh, and in many species are constantly replaced throughout the shark's life. When they lose a tooth they will replace then within 7 to 8 days. All sharks have multiple rows of teeth along the edges of their upper and lower jaws. New teeth grow continuously in a groove just inside the mouth and move forward from inside the mouth on a "conveyor belt" formed by the skin in which they are anchored. In some sharks rows of teeth are replaced every 8–10 days, while in other species they could last several months. The lower teeth are primarily used for holding prey, while the upper ones are used for cutting into it. The teeth range from thin, needle-like teeth for gripping fish to large, flat teeth adapted for crushing shellfish.
A shark can have hundreds of teeth in its jaw. Sharks, as well as other Chondrichthyes, have the ability to replace their teeth if they become damaged during feeding or fall out due to natural causes. Many icthyologists have suggested that sharks can lose tens of thousands of teeth within the span of a few years.