An anti-theft device would look very different than one of these tags. It would have to be hidden, difficult/impossible to remove, etc.
Sure, these aren't the ideal anti-theft device, but they're a lot better than nothing?
I mean, I could easily hide one of these in a framed oar-raft or the raft trailer or a sea-kayak or my old cargo van or even in my bikes seat or in a backpack of climbing gear...
...sure, a thief could find it, but I'm a good hider! And they don't have infinite time because they're being tracked! And if they do find it then they know they were tracked!
The real anti-theft tech just is too expensive and bulky to realistically use like this...?