You have to ask just how stupid some of these people are. There would appear to have been multiple attempts to contact them which have come up dry, and only then to the police come knocking. Surely if you were minded to ride your luck, once you'd had a couple of calls and presumably not responded you'd think your luck had probably run out, and start quarantining as you should have been in the first place.
I don't agree this quarantine thing is a particularly smart policy, but again, it's the law, not optional and if the law is flouted, to a point where the police have to become involved then a fine should be the logical result - in every instance. It's hardly fair on those who do comply with the rules for those that can't be bothered to get away with a slapped wrist and suffer no penalty.