I agree it's best to be in possession of all the facts, like if you were sitting in the court.
But, 99.9% of people who hear about the outcome of the case weren't in that courtroom. All they heard reported was
- owner of land allows bulldozer to destroy irreplaceable prehistoric monument (whether deliberately, negligently, ignorantly, carelessly, or whatever)
- owner of land gets fined relatively paltry amount
- world keeps turning (without irreplaceable prehistoric monument)
Don't you have to consider the example it sets to other people who have prehistoric monuments on their land, who might find them inconvenient, and might then weigh up the cost of paying the fine for the convenience of making it easier to plough the field (or whatever reason one might have)?
Big fine = deterrent
Relatively small fine = well maybe it's worth the hassle