They do. The Prius is overrepresented "because their catalytic converters contain more unused precious metals than standard gasoline-powered vehicles" [1].
> Why isn't it a problem in other geographies?
It is [2]. It's just a bigger problem in California [3].
1. some cars are easier to get under, or have more expensive cats (hybrids fit the second category)
2. cats are usually traded for drugs, so such operations are more common in areas with more drug problems (the kind of people who can recycle them tend to have drug connections, and the kind of people willing to grab them tend to be addicts)