USPS & US Customs

USPS service on a registered mail from Denver, Colorado to California took 9 days! Why? This peice of mail from London (contents arestamps, of course) is held up in the US Customs in Los Angeles since Feb 9! Why?
Tracking #:RN086584258GB
Carrier:Royal Mail
Status:ACCEPTEDIN TRANSIT
Processed Through Sort Facility
2015-02-09, 11:06:00, ISC LOS ANGELES CA (USPS)

It happens all the time, even with regular mail that is other than ordinary letters. Packets and parcels get extra attention. One possibility is this packet was in a mail container that had another packet in it that had drugs in it, and the drug sniffing dogs hit on that bag so every piece of mail in the bag was examined though most were not opened, before it was released. Another possibility is the X-ray machines detected something in that container of mail that was suspicious and everything in the container had to be searched. Or it could have been a container of mail that was tagged for a random search by customs to check to see that everything had its customs taxes paid, or perhaps some other situation. I once had to wait 2 months for a packet of stamps to get from the Netherlands to Maryland and there were no issues with my stamps at all. The US is ground zero for petty crime, serious criminals and terrorists to try to attack and the resulting slowdown in international shipments of all kinds is the price that is paid.