the code that landed humans on the moon has 72k stars on github and your startup's monorepo still can't pass CI on the first try

Not the same goals, risks, monetary budget, time budget.

If your goal was to absolutely prevent any errors and you would go great lengths to do it, you would.

Just look at any safety critical systems: medical, transportation. There has been some incidents, but some systems do work really well that are developed today.