You are comparing oranges to apples. FedEx, UPS, etc., do not visit every single PO address every workday and do not have the economy of scale. They also have extra overhead the USPO can ignore, like registering and tracking packages. FedEx cannot require each delivery address to provide and maintain a delivery box at the recipient's expense; USPO can and does, which decreases their cost. And since the average volume of an item delivered is bigger (typically a box instead of a letter), FedEx/UPS are forced to use larger trucks at a higher cost.
USPO could have, but didn't, offer services like overnight delivery until they felt the competition from FedEx, which was the forefront of technological advance. USPO has always played catch-up.
Even with these differences, FedEx/UPS make twice the number of trips to my neighborhood as USPO; once to deliver in the AM, once to pick up in the PM. Sometimes they have multiple trucks to cover the same area. My single mailman comes by only once per day, even at Christmas.
And just to nitpick: your ".44 cents" is wrong, and 100 times too small. USPO charges .44 dollars per letter, not .44 cents.