Ironically extreme programming (the first real iteration of Agile) was big on getting requirements, creating what some call spikes (POCs of concepts or demos), and talking to stakeholders as one of the key priorities.
The chunking of 2 week sprints is a natural result of this, where the idea is you get together alot in the first few days of a sprint, plan some loose but defined stuff, iterate on it, come back for a day or two in the middle, re-iterate, and then show your work and plan the next cycle. Work should be introduced in such a way it can be chunked in small pieces like this.
This is why TDD became highly coupled to Aigle/XP by the original practitioners around Agile development. Tests are your first validation of an idea, a way to write code-as-documentation and feature validation, before you actually implemented the thing in the product line. (side note: TDD has bee distorted too, by both "zealots" and the opposition, largely lost its original intent and execution)
The real problem, as I have observed, is that everyone is still waterfall or some version of "waterfall lite" and doesn't actually observe the intentions behind Agile. Its been completely devoid of the meaning behind the original manifesto. Hardly any place follows it in its true form, I feel.