Not a proper summary (it's a long article), but here a few high points, in random-access-memory order.
The vast volume of consumer products shipped by Amazon and Big Box retailers represent a tempting opportunity for thieves. In the old days, thieves were after cash and easily-fenced valuables. Today, consumer products are easily fenced. In fact, products stolen from Amazon shipments are sometimes resold by other vendors on Amazon!
Thieves range from casual/opportunistic to highly organized (with warehouses, etc.). Labeling on containers offers clues to thieves as to which are best to rob. No one wants a container full of kitty litter.
LA is the worst place for this, because of the largest volume of shipments goes through there.
Containers on trains are especially vulnerable, because trains are long, and crews are sparse. The trend towards long trains makes this worse. More sophisticated thieves will climb on trains and cut the air, forcing the train to stop. They'll offload what they can before the crew or the law shows up.
Containers are generally poorly secured (locks easily cut). The container providers are indifferent to this. Insurers, on the other hand, are VERY distressed and motivated to work with law enforcement. Bait containers are now a thing.
It's not just trains. Long-haul trucking has the same problem, but with higher risk to the crew (driver).
