>How would you build a rocket if you only thought about the next 2-4 weeks?

We're not building rockets. We're building business software. And the requirements for that are not a hardline set of rules laid out by the laws of physics. They are soft and fungible. Beholden to the whims of a product manager, designer, or client. Generally almost nothing is truly understood about the shape and function of the resulting software at the beginning of a development process. And sticking to a "plan" that was laid out before these things have actually been discovered is a recipe for disaster. Better to build in tiny, discrete chunks of usable MVP that can be used as a guidestone to the next desired level of functionality.