There’s no need to have market based competition to keep costs down. Look at USPS for example. That operation is run without a profit motive, serves literally every zip code in the US (by definition), and runs healthily year after year (except for the part where Congress imposed arbitrary pension funding requirements[1] and private capital interests have been chomping at the bit to buy up all the real-estate holdings).

They also don’t have UPS’s problem of not putting AC in their delivery vehicles.

[1] https://ips-dc.org/how-congress-manufactured-a-postal-crisis...