Everything about American cities makes more sense when you realize they are designed entirely for cars to go fast. That is the sole metric and everything is optimized to sure cars can go as fast as possible no matter the cost, both literal and less tangible.
Take the Evergiven. It can fit ~20k containers. A “quick” check each going 2 minutes would add 40k minutes to loading, or 667 hours or 27 days. A month basically.
In a world where time is money no way they are checking all containers.