My understanding is that the context in which the pieces are found is of enormous import to archaeology. It would be better to one site done properly with the rest in the ground than lose the context from a larger number of sites when the artefacts donated anonymously.
Your understanding is correct, though I believe that you, jordanb and me are tilting at windmills (as most commenters seem to think the laws are insane without even trying to understand the dynamics behind them). The allure of the fantasy of a real life treasure hunt is too strong compared to the boring reality of field work and research :)
But do you understand, that most people are not deeply fascinated by archeology to just let some people dig up their yard or make them wait unspecified time for their new home to be build for some years without proper compensation?
I am deeply fascinated by archeology, but I do think it is insane expecting this of people who do not share my fascination. And the result is likely, most artifacts and sites get lost.
Why? If you make a law, that people get a finders fee if they find something of historic value, only if they stop digging after finding it, but get a fine if they do destroy the site, how would that make more destruction?
Harder is it for homeowners, because real compensation there costs real money - but how else would you compensate people for individual loss, for the common benefit (research)?
Not if it compels them to hold their land fallow for an indeterminate months or years, in exchange for a one-time payment (or none at all). I’m all for proper archaeology but I can’t expect those who are trying to use their land to prioritize it unpaid. I don’t expect their government offers enough social support and compensation for the lost time to make it worth the risk and annoyance.