Another approach would be to focus on patients and ignore punishments. Which is what the hackers are doing: ignoring rewards and punishments that are driving professionals in the field.
One of the things about testing drugs and medical devices is, you really can't cover all your bases. It would be too expensive to construct a clinical trial with the statistical power necessary to reliably detect very rare side effects. I don't think anyone wants to delay releasing all new drugs to the market by 40 years so that we can be sure about what happens if you take it over a lifetime. Even post-release monitoring for these things is potentially tricky, due to the poor interoperability of EHR systems and also, in many jurisdictions, unintended consequences of health care privacy laws.
Meaning that there is no amount of due diligence that will guarantee you can't get sued. Which is fine, you can always go for proportionality instead. But then, the amount of due diligence that's necessary is driven by what costs the legal system is willing and able to impose, and, at least in the legal regime I live under (USA), they've got their own entirely other set of procedures and incentive structures that they're working with.
Also, the amount of insulin used is not significantly different with a closed-loop system vs. not. Although closed-loop systems do increase the benefit of faster-acting insulin relative to slower insulin, and the fastest-acting insulins are more expensive (especially inside the US).
For better or for worse, in an environment where "root cause attribution" is such a preoccupation, it's not such a stretch to think that the agents acting in it would be strongly incentivized to minimize their opportunities to be the root cause - in other words, "be blamed if something goes wrong".
I don't think that needs to be interpreted as nefarious. It might just be that everyone looked at making them more automatic, and just decided that the costs to do all the research that would be necessary for CYA and regulatory purposes would be too great.