I've never had a package stolen. Even when I lived in a sketchy apartment years ago. If it's a high value item I either have it delivered to me at my work (this is a privileged position to have, I know) or get it delivered at an Amazon locker a mile or two down the road.
Would it be a pain in my ass if I lived in a high crime area, worked somewhere that didn't accept my deliveries, and relied on public transport? Absolutely. But I'm guessing that's not who the majority of Amazon's customer base is.
It's one of those opportunity crimes where the easiest victim generally picked. It usually comes down to just two things:
How many people see your porch
How easy is it to walk up and walk away?
You'd be surprised how much of a deterrent a mild inconvenience is. You'll get significantly fewer packages that walk off if you live on a big hill, or have a bunch of steps, where it's mildly inconvenient for someone to walk up.
I lived in a high crime area and I still didn't have any packages stolen. I lost more packages to the delivery person delivering it to the wrong apartment versus porch pirates.