Of course they do. You've heard of taxes, right?
And who decides what the stuff is worth? Would that be the free market or the "experts" at the museum?
Do the finder and the landowner get to refuse the museum's offer if they think it's too low? And would that be a private or government museum?
And what if the finder and landowner really like the stuff and want to keep some or all of it for their respective "collections"?
There might be VAT tax due immediately on the appraised value of the stuff. That would effectively force the find to be liquidated.
The right way to do that would be to consign it to an appropriate auction house so that museums and private buyers could compete in a fair and open process.
One advantage I do see with the law is that it would tend to prevent disputes between the finder and the landowner which could be brutal if a lot of money is involved.
I used to work as a commercial numismatist, they go off the values published in the latest ‘Spink’ catalogue, not some made up figure they pulled out of their arse.