Nobody's home during the day. What neighbor? How do you know which neighbor will be home, or which neighbor to trust? When 90% of your package recipients are not home, you spend 3x as much time per package delivery.
Carriers offload responsibility by allowing the sender or receiver to opt-out of signature/package acceptance, so why would they care?
Just one data point, but I've been having packages delivered to my home my entire life and never had a single one go missing. Seems like a really high cost to prevent something unlikely.
On the other hand, I had never had a home or vehicle broken into until someone smashed my car window last night at the movie theater. So, there's a first time for everything.