WHY do elaboration and self-explanation work?

Generating explanations forces you to integrate new material with existing knowledge (schemas), creating more retrieval routes and exposing gaps.

A schema is your organized web of prior knowledge on a topic. When you explain how a new fact fits that web, you're not just storing the fact — you're wiring it into a structure, which gives future recall many possible paths back to it instead of one fragile thread. The effort of explaining also acts as a diagnostic: the moment you can't finish an explanation, you've found a gap you didn't know you had. So elaboration both strengthens what you know and reveals what you don't.