@Ginfordinner
In some areas a parcel left on the doorstep might not be there when you go and pick it up a couple of hours later.
Where we live it is a massive inconvenience to go and collect a parcel from the sorting office. Is this even allowed right now? Having it redirected to the local post office cost £1.50 last time I used this service.
I just find it easier to answer the door to pick up deliveries. It only takes a few seconds. Although, in reality DH usually answers the door when I am working as his office is by the front door.
I live in 2021, and like the vast majority of people, I know when a parcel is expected. You often get a notification to the nearest 2 hours it's due. So I will look out for it. Same with any other 'delivery.' If it's my birthday, I will (again,) be on the lookout, because I usually get flowers, and several packages... Apart from that, I will not answer the door if I am not expecting anything, (or anyone...)
And I live in a nice quiet rural area where nothing is ever stolen off doorsteps. You must live in quite a rough area. Maybe you should move.
Also, these days, you have a facility to create a safe space for the courier/postie to drop off your parcel. Mine is my shed. You obviously have the internet to enable you to do this, or you wouldn't be posting here.
Why would you go all the way to the sorting office when you can easily allocate a safe space to leave it near your home? You can even arrange for it to be delivered to your local Argos or Morrisons or similar, where you can pick it up at your convenience...
Why make life so difficult for yourself? Why on earth would you answer the door to every single knock? 
You seem quite agitated and annoyed that people do things differently to you. Why is that? So, not everyone likes to answer the door to every Tom, Dick, and Harry. So what? 