If you want concrete examples of baggage claim existing outside of the secure zone of an airport there are plenty, but these only usually occur in domestic terminals. E.g. Every Australian Airport, NZ Airport, LAX domestic, JFK domestic can all be accessed by the general public. (these are all airports I have travelled through btw)
Baggage claim is generally put behind security when the port of arrival is serving as a first point of entry to a country, and thus requires customs to be cleared etc. As @me123 has said, it’s actually got nothing to do with risk of theft.
That said, I do of course agree that there should be later facility to build secure baggage too, but that will come 