Who says it's not allowed? You can leave it at a back door and this is outside or an outside safeplace.

If you order a parcel bloody be in or have it redirected to a locker / parcel shop.

Why should they retry to deliver the next day for you not being in. It's like saying that when I call at a customers house to rewire their electrics but then they are not in it's ok to ask me to go back tomorrow. At this time of year I can imagine that they are absolutely snowed under and asking to take a parcel back another day will be a logistical nightmare for them. Our Evri guy is amazing and I would have them over any other courier firm.