It's not unknowable; FedEx and UPS at least will reattempt delivery every day for a certain number of days before giving up. At least that's the case in urban and suburban environments. Maybe you live somewhere rural where their policy is less clear?
> It's difficult to figure out exactly where the facilities are
No it's not. The tag they leave behind will often tell you, or you can enter the tracking number online and it'll tell you there. And usually it's the same place every time, so once you figure it out, you're good for future packages.
> and you're not guaranteed the package won't still be on the original truck or on a new one
This is the annoying thing. It's never clear when the package will actually get back to the facility (after they failed to deliver it to you), so you don't actually know if it'll be there when you show up. Many many years ago it was a simple matter of giving them a call, but nowadays you end up in customer support / phone menu hell, and it's incredibly difficult to talk to someone who is actually physically present at the facility.
> The main reason we are cool with deliveries being left on the porch isn't that we trust our neighbors, it's that the alternative is so much worse.
I'm absolutely not cool with this. I trust my neighbors just fine, but I don't trust all the random people who might be walking around, specifically looking for packages to steal.
I'd much rather have to drive over to a facility to pick up the package, or just wait until the next day for another delivery attempt, but most delivery drivers don't give me that choice.
If the package does get stolen (incredibly likely, if it's left outside), I'll usually have to wait several days for the merchant to ship a new one (because they figure it's possible it wasn't stolen, and want me to wait and see if it still gets delivered in a day or two). And then I have to wait for another shipping-time cycle.
