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)
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.