It is to do with getting permission ,and luckily it is not just handed out to serve our curiosity .

We have seen how much damage we have caused in the past by destroying imortant evidence due to our ignorance and unsophisticated approaches . To dig now is to destroy something that future generations will see as destruction ,just as we view the destruction done by barrow diggers of the past .Just as out understanding , techniques and technology are far more sohisticated than that of even thirty years ago the attitude is that we should leave well alone except when necessary i.e. when developers are going to build .
Dosh is also important but it's the philosophy of leaving something for the future and not destroy evidence and sites that is most important .