Buildings typically use a safety factor of 1.5 to 2.0, and cars typically use a safety factor of 2.0 to 3.0. These things are being built twice as strong as they need to be. I wouldn't call that narrow.
And with software, we're at a point where it can't even properly do what it needs to. If we were overbuilding it, damn software wouldn't crash so much.
Not even close.
For example, a BMW X5 weighs about 2200 Kgs without passengers, and it's GVWR is 2800 Kgs.
If you have five people and heavy bags, you can comfortably exceed the GVWR. You can absolutely break control arms and suspension components in that scenario if you go over a speed bump or hit a pothole (which are real things that exist in the real world, like people doing something unintended and crashing software).
If this needed a 2x safety factor, there would have been no way to build this car.
Even the toughest cars like land cruisers are limited in this way.
> [...] vs something that's rickety
A 100 percent of modern bridges are rickety. There has been dozens of high profile incidents because of this.
> Just because you built something that might fall apart at any moment doesn't mean it's been engineered with narrow tolerances.
Here the software they are building falls apart in ..say.. two days of use, but can be updated in 5 seconds at close to zero marginal cost. The software is useful enough that people keep updating and using it. This iteration gives them a competitive advantage over the safer choice of rigorously testing every new thing for several weeks.