The low hood is almost definitely to help prevent scraping mailboxes and other objects, but especially mailboxes. My dad was a rural USPS carrier that used his own vehicle, and despite him having been an excellent driver with no accidents on record in his life, he still ended up swapping minor paint with mailboxes a few times.

Can't imagine how often it happens across the country.

The low hood is almost definitely to help prevent scraping mailboxes and other objects, but especially mailboxes.

The USPS states that it's to keep from hitting pedestrians.