From Apple's AirTag page:Have Apple explicitly said that though? I think we're all, quite reasonably, inferring it given how bad at tracking stolen items these tags would be, but it's odd that one of the questions to Apple wasn't "so what about tracking stolen things?" so that we can hear their rationale in their own words.
AirTag is designed to discourage unwanted tracking. If someone else’s AirTag finds its way into your stuff, your iPhone will notice it’s traveling with you and send you an alert. After a while, if you still haven’t found it, the AirTag will start playing a sound to let you know it’s there.
Given it would be impossible for Apple to design a system that could distinguish between tracking an item that a thief doesn't know has a tag and tracking and item that an unsuspecting victim of stalking doesn't know that have, I think it's reasonable to conclude that Apple choose to prioritise preventing unwanted tracking over tracking a stolen item.