Why is it illegal for amateurs to dig up items at an archaeological site?

It isn't always illegal for amateur archaeologists to dig at sites and in fact, many new sites are discovered by amateurs. Generally, those in charge of a site will prefer experts to work on the site and simply not allow amateur volunteers to be present. In other cases, voluntary assistance from amateurs can be welcomed.

In some states and countries, there are legal restrictions on digging but they vary significantly from one to the next.