It varies greatly depending on where you live. My sister lives in suburban Maryland, and leaving a package outside on a porch is just no big deal. The probability that it gets stolen is actually ridiculously low. In this case the high trust is completely warranted.

I live in San Francisco, and if a delivery person ever leaves a package outside, it's always a scramble to either get there to take it in, or find a neighbor who can do it for you. (I live in a 4-unit condo building, so we all try to look out for each other's packages when this happens.) It's just bizarre to me that delivery people aren't specifically instructed to never leave packages outside here. I suspect they may be, but they're overworked and don't want to have to add yet another package to their delivery schedule for the next day. And/or they may be evaluated on number of completed deliveries, no idea.

(On the flip side, there are some neighborhoods in SF where it's ok for a package to sit on a doorstep for a while. Not many, but... they exist.)