How do you reconcile how bespoke and ever changing the requirements are for software products vs how stable the requirements are for garages?

I'm asking because I see the construction analogy pop up a lot and I just can't reconcile the two things.

To me the development of a new blueprint for a new kind of garage for a new kind of vehicle operated by a never before seen alien species is a bit closer to creating a software product.

I mean, who would ask a contractor to do what people regularly ask software engineering teams to do?