Who uses USPS? Well, FedEx and UPS that's who. As of a year ago FedEx was the USPS's largest customer, as a very large portion of their packages they depend on USPS to make the final delivery. FedEx's Smartpost and UPS's Mail Innovations services depend greatly on the USPS and give it a ton of business. Not to mention the APO service they have totally pwned, and the INTL shipments that USPS can somehow get things into places nobody else can, with little or no paperwork. I used to work at a small business that shipped 3k-5k small packages a week, and USPS was very very competitive with the under 1lb, and pretty close on some other stuff. 6 days a week is silly, and I'm sure there's tons of waste (ever been inside a post office? LOL!) but the political crap has already been mentioned.
And with regards to UPS and FedEx sucking, a lot of that has to do with your driver. I've met plenty of drivers that were very hard-working, considerate, upbeat, and friendly. Some are total garbage. They should be bagging items if it's raining/wet, and if you leave instructions to leave the pkg. at an alternate location, "on the porch/around back/etc" they will in my experience.