If they ship millions of containers, surely they can work out an efficient solution.
Yes, at some point they need a lawyer and what not. But not every single time somebody wants to ship a container. They work it out once and that's it. Even if the lawyer costs 100 million dollars, if they ship millions of containers every year, they can scale the cost down to one dollar per container in the end.
The system to only ask for money in case of accidents doesn't actually make it cheaper or less complicated. There simply is the inherent "cost" (a ka expected loss) of accidents, that you have to pay one way or another. There may also be people who don't want to pay, and then you still need your lawyer.
My travel insurance is very cheap, by the way.
Insurance is an old and established business, many learnings already exists. The industry presumably is quite good at estimating and pricing risks.