If someone steals your AirTagged device, after it's away from whatever you paired it with for a while, it'll start beeping, which will quickly alert the thief that they need to find the AirTag and throw it out. So I don't think AirTags were meant to deter theft; I think they're just there to help people find stuff they've misplaced.

I think the marketed goal of AirTag isn't to prevent theft, it's to help find lost (but not stolen) objects, like if you left your keys somewhere.