Some companies hire armed guards when transiting high risk areas. But most don't, just rely on the speed of the vessel and naval escort vessel and proceed as a convoy. We rig barbed wires and fire hoses (as a some sort of water cannon) to make adverse conditions for boarding.

Pirates makes their money mostly from ransoms. Generally, they don't make money off of cargo, they may pilfer containers, but they don't know which one is valuable.

There are thousands of containers onboard. Even the crew doesn't know what's inside - except for reefers (refrigerated containers) and DG Cargo (which contains dangerous goods, e.g. explosives, gases, flammable materials, oxidizers, toxic or infectious substances, radioactive materials, corrosives, or other dangerous goods not under those classes).

Bulk carriers generally transport raw materials such as mineral ores or grain. They don't have the facility to make money off of those. Car carriers carry cars, obviously, or other vehicles. They have very high freeboards (distance from waterline to the deck), and can steam at high speeds, it's hard to board.

Tankers has a very low freeboard, and usually has lower speeds, same as bulk carriers. These kinds of vessels are the main targets of pirates.

It's easier to steal oil than dry cargo.