Unable to deliver is due to restrictions by the post office not UPS or FedEx the post office has out lived it’s usefulness due to unions over costs.
The suppliers are shipping UPS not USPS. That’s why I can’t get certain items. Since Amazon went to shipping direct from suppliers instead of from Amazon itself I can no longer get a lot of items.
At least with FedEx they transfer in Anchorage to the USPS and I can get items shipped that way but most Amazon clients are UPS shippers.
When I shipped model airplanes in California I had to stop using UPS because of damage. USPS beats them hands down. FedEx is too expensive.