Many standard rate FedEx and UPS parcels go to a “fulfilment” service, which often uses USPS to finalize the delivery. This is particularly true in rural areas where FedEx and UPS don’t have frequent routes. This means your letter or package has to compete with all that stuff from the private carriers. I don’t know how the shutdown is affecting USPS, but I know they hire seasonal mail handlers this time of year, and that may be disrupted.
