It is the method of last resort, really. Ideally, people have enough success in their life that they do not have to resort to crime. If that fails we have some other protections: we lock our doors, etc. Lastly, if people still commit crime we try to prosecute them
And for good reason. These devices are already getting popular with abusive spouses. It's worth planning for the worst case scenarios for these things, because they are real.
Realistically you have to be much more determined to buy an additional phone and another sim card + pay for the data vs simply using an airtag. If you're already that determined just buy a proper gps tracker.
You'd also have to find a way to recharge the iphone constantly, problem that you wouldn't have with an airtag. An airtag is much easier to hide too (bags, clothes, ...)
The fact that you can already track someone relatively easily doesn't mean that introducing a new small/cheap/easy to use tracking device is a good thing
It's not designed to be used like that
> Why do we have to gimp everything to make it difficult to use them to break the law?
Same reason you can't buy 1000kg of fertiliser at walmart, we don't wait for people to commit crime to do something.