I keep mulling over decisions like this, and I think the fundamental clash between the hacker ethos of repairability and the corporate ethos of products with well-defined failure modes comes down to a clash of innate human values with capitalism.
Capitalism fundamentally does not view human life as sacred. Or rather, it puts a finite value on human life. The bond between a mother and son is priceless, there is (in the case of a loving relationship) no price that either would put on the life of the other. That is to say, there is no amount of money that either would accept in exchange for the death of the other. As actuaries know, this is not true from a capitalist viewpoint. The value of a human life is frequently calculated by various means to be somewhere around 3.5 million dollars at birth. Which is to say, if a policy change costs an organization (private or public) over 3.5 million dollars to save one human life, it does not make financial sense. So when you look at a decision by an automaker to include a "safety" feature, you have to ask "did the amount of money that this costs the company work out in terms of human lives". In this case, BMW likely concluded that the financial damages of settling an insurance claim for a battery fire, and damage to their brand from the massive negative publicity of battery fires (see Tesla) would be more than the cost of implementing this "feature". This is also true from the legally mandated standpoint of crash safety features, which result in cars being much easier to total because of crumple zones. The cost of a $100k vehicle is much less than the cost of a $3.5 million human life. On the other hand, the carbon and pollution cost of replacing many $100k vehicles is borne by the public. An interesting view of this topic is summarized in the Wikipedia article "Value of Life" under the heading "Uses", which specifically covers the cost of implementing emissions regulation vs. the cost of the human lives that reduced emissions would save. https://en.wikipedia.org/wiki/Value_of_life#Uses
As has been pointed out many times, vehicles these days are cost engineered to last as long as the average buyer of a new vehicle will hold onto the car. Since BMW targets a luxury market, that lifetime is likely on the order of 4-5 years. A Toyota is probably closer to 10 years. Automakers do not (as far as I know) make a meaningful amount of money on the maintenance of used cars; OEM parts do not necessarily come directly from the automaker, but rather a company that contracts with them or a subsidiary whose financials are not counted as part of the manufacturer's bottom line. Therefore, in our modern era of late-stage capitalism, companies have no incentive to make cars that last longer, and complaints from customers who wish that their end-of-life cars were easier to repair will fall on deaf ears. Those of us who wish our cars were less "safe" in order to contribute less to the criminal waste of disposal of otherwise sound vehicles and carbon cost of making a new vehicle would do well to consider the financial calculations that went into those decisions. Is making batteries that are easy to fix but kill someone when improperly repaired in 1/1000 crashes more ethical than installing systems to prevent batteries from ever being misconfigured? Are there more BMW crashes than other brands due to the target demographic? Is the number of batteries that will be repaired improperly significant enough to cause a large number of battery fires? I don't know.
This is by no means an excuse of these practices, but merely an attempt to understand them. I would love to hear where my reasoning is flawed so I can better understand this. It certainly seems to me that the risk of a shade tree mechanic soldering a piece of wire into a BMW battery computer is astronomically low, but I have seen repairpeople of all shades do really stupid things to save money so probably not zero.