Bunch of things.
* The privacy/safety tradeoff is different between the two kinds of crimes. There's a distinction between computers passively collecting data and humans actively investigating (and stopping) cars.
* Violent crimes are the local enforcement priority, and if you give police tools to clear non-priority crimes, you are changing their incentive structure.
* The link between the car and the crime is especially tenuous in routine property crime; it's just as likely we'd be stopping people's mothers and grandparents as that we'd be stopping actual criminal suspects. That's obviously not true with a carjacking.
* Being specific about the crimes we want to apply Flock to makes it easier for us to track (and, much more importantly, talk about) whether the cameras are successful. It's a real mixed bag right now!
Having said all that, the pro-camera contingent certainly does want Flock cameras used to catch package thieves and shoplifters. But they were up against anti-camera people who wanted no cameras at all. We took the opening and set our own terms.
Going after "easy" stuff like traffic and parking violations (neither of which can be enforced using Flock cameras here) is definitely not a problem we have. Our municipality is extraordinarily safe, but it's nestled into one of the less-safe areas in Chicagoland.