2. We have a general AI exception handler called a pilot.
3. Many of those systems have hardware redundancies, so even if there is a bug, hardware can stop it. A fuse might blow instead.
And you get a refund for your plane ticket if you reach your destination, but if you don't, whoever figured out the trick to crash the internet-connected plane gets to keep all the ticket money. And that could be the same person who wrote the plane's software.
The incentives to break those other pieces of software are different.
Very few people are incentivized to hack planes to crash and kill people. Even fewer are incentivized to hack the space shuttle. Not to mention those pieces are rarely exposed on the public internet, or have connectivity at all.
But massive amounts of nigh-untraceable free money? Ton's of people are incentivized to go for that.
It's hardware with no joysticks for humans to adjust. It just happens to be hardware that's implemented in code.