The reason there are so many projectile points to be found, even after centuries of determined collecting, is that the technology is a very old one: people have been making points to hunt animals for over 200,000 years.

What makes an arrowhead valuable?

Arrowheads are worth more if they are very ancient or made out of unusual materials. An arrowhead (or more likely a spearhead) that is 10,000 years old might be worth a fortune. Arrowheads made of gems such as japer are worth more than typical grey stone arrowheads.