So the defense for software is "I helped build a system so complex that even attempting to determine how it might fail was too hard, so it can't be my fault that it failed"?
Unless you want to go back to the steam age, it’s not a defense, but all we are humanly capable of.
Never forget as well that it only takes a single cosmic ray to flip a bit. Even if you code perfectly, it can still fail, whether in this way or countless other black swans.
2.8 trillion lines of code aren’t going to rewrite themselves overnight. And as any software developer can tell you, a rewrite would almost certainly just make things worse.
The cost plays a very important role in building codes, a lot of changes are either not made at all (because they will be prohibitely expensive), or spread out over many years.
Plus, the bulding codes are safety-focused and often don't cover things that most people would consider defects: for example a huge hole in the interior wall is OK (unless it breaks fire or energy efficiency codes)
Not at all, you can have that today if you are willing to pay the costs of providing these guarantees. We know how and some organizations do pay that cost.
Outside of those rare cases, everyone is demonstrably unwilling to pay the unavoidable costs of providing these guarantees. The idea that software can be built to a high-assurance standard by regulatory fiat and everyone just gets to freeload on this investment is delusional but that is what is often suggested. Also, open source software could not meet that standard in most cases.
Furthermore, those guarantees can only exist for the narrow set of hardware targets and environments that can actually be validated and verified. No mixing and matching random hardware, firmware, and OS versions. You'll essentially end up with the Apple ecosystem, but for everything.
The vast majority of people who insist they want highly robust software neither write software to these standards nor are willing to pay for software written to these standards. It is a combination of revealed preferences and hypocrisy.
