In other countries (like Italy where I currently live) leaving a package unattended is unthinkable. If there is nobody home they leave a slip of paper that says there will be another attempt at delivery the next day or else you have to fetch the package in some remote dispatch center (things are getting better now and many couriers are now taking their time to call you on the phone a few minutes before they drop by; sometimes you can ask them to drop the package at neighbors or at some small shop nearby, if the owner is willing)
Yes. You are just probably too used to it to notice.
Decades before it didn't happen as often in places it does now (yes, it did happen in other places. No excuse for a neighbourhood to go bad though, e.g. through tons of meth/opioid addicted piling to the crime rate).
In nicer neighbourhoods it doesn't happen still.
In whole countries (like Japan) it's unthinkable.
>Leaving aside small sleepy towns, everyone locks up their house, car, bicycles, and other possessions, even the people complaining about stolen packages
In my place (like in places like Tokyo or Singapore today still) we used to sleep with open windows, and had no problems even living cars unlocked. So there's that.