I suspect a combination of effects, but at least part of it is probably deliberate. Real covid virus has a half life of 18 hours or so, at room temperature, in the shade. Say some Chinese worker coughs covid onto a product that is then sealed warm, safe, and dry, in a cardboard package and shipped overseas. After 21 days or so days there is no detectable trace of any virus contamination. So you keep the packages backlogged in the system, sitting in boxes, waiting to move. It has the same effect as a deliberate quarantine policy, without the official enforcement burden. No need to inspect every package either, just delay the whole ship. Just like black plague times. So what do you do if the virus is already in your country? Same thing, just gum up the shipping of everything back and forth. Delay delay delay, everything. This cuts any virus spread via surface contamination down to zero.