By having it on a card that is signed it means there can be no confusion as to what was declared upfront.
Also they do serve as a reminder to think about what you packed, I know I do a mental double check of my bags and work out if I'm going to declare or dispose of anything when I get the form.
The problem with the "slimmed" yellow arrival cards is that unlike the old quarantine declaration form which was on a large three-fold brochure is that there's no information on the card which makes a point that this is important. Yes, you can read up about travelling into Australia online at your equivalent of Smart Traveler; yes, you can learn from experience (perhaps a fine or prison sentence has taught you); yes, there is usually a video that is screened before arriving in Australia.... but at least on the old three-fold, there was a very large box with clear text (something along these lines):
If you are unsure if you have it in your luggage, or are unsure if you have to declare it, tick YES - DECLARE IT
Now, there is just a tiny text on the top which says: "ANSWER ALL QUESTIONS. IF UNSURE,
[cross box] YES"
It's not awfully clear. Well, I lie. It is quite clear. What it doesn't communicate is how important it actually is to answer truthfully.
People understand easily, without pretext, that lying about your name is not a good idea. Most people going to almost any country in the world don't really understand that lying that you have food packed is a big deal when you enter Australia.
At least countries like Thailand and Singapore, with their incoming forms, make it quite clear that amongst other things, trafficking drugs is punishable by death. If Australia had a similar thing, I think it would be wise to make sure that is clearly communicated on the yellow card (though suffice to say if you were carrying drugs and you only found out this fate by reading the card on the plane, you probably deserve to be put to death).
Customs can keep the form as is, but in doing so, they risk catching more people who have simply misunderstood. If that's the only way they can fill their quota of fines and imprisonments, then so be it.
To be perfectly honest, if they really want to be
that serious about quarantine to the point that people think the process is not being abused and people are falling through the cracks, then they would have to basically turn customs into a process which could be almost like a cross between attempting to enter the USA and filling out your US income taxes for the IRS. Except they would also get rid of the "Nothing to Declare" lane. Everyone would be benched; if you got the form wrong, instant interrogation room - doesn't matter if you just forgot, or you cannot understand the form, you get the room, and a high chance of being fined as a minimum. Breaches over a certain weight of food (or wood or whatever) or matter regarded as dangerous, especially if not declared, attracts mandatory detention or immediate deportation.
Oh, and while we are at it, since we've just had a corruption case within the customs officers ranks, I would propose that all customs officers who are found guilty of breaches like corruption face mandatory prison sentences and cancellation of any job benefits accumulated whilst a customs officer (e.g. superannuation seized). That would be the check and balance so the Gestapo aren't necessarily above the law.
I'm sure that will probably put customs officers on the same hit lists as parking officers, telemarketers, and about 99% of politicians. But.... you said we had to get serious about it, right?