According to icontainers.com, only 2-10% of all shipping containers are inspected.
What is the rationale for very thoroughly searching passengers and their belongings for drugs, when a simple opening of the bags could indicate that the passengers isn't carrying drugs in bulk? Given that the majority of shipping containers aren't controlled, this seems like a hugely disproportionate effort.
Edit: As pointed out in the comments, the rate of passenger searches is orders of magnitude lower. This source claims about 0.07% of passengers are searched:
Approximately 140 million passengers entered the United States on
international flights during the two fiscal years 1997 and 1998. From these
arriving international passengers, Customs inspectors selected about
102,000 passengers for some form of personal search.