Earlier quoted context omitted.
Why must it? Why not have they work only with 80% reliability if it could lower the price and put it in the hands of way more people?
Because if it had 80% reliability it wouldn't be a safety device at all. Think of cars, would you buy at a very discounted price a car whose brakes would fail 2 times out of 10? Different contexts, I know, but when safety is a must price doesn't matter much.
As of a decade ago, incorrect airbag deployment killed one person for ever 7 lives it saved. Nonetheless, they were mandated by law for many classes of cars, and were purchased voluntarily for others. And this was the right decision. They could have spent thousands of dollars per unit to get the mistake rate even lower, but that wouldn't have been worth the money.