Necessity is the mother of invention. MapReduce-based systems were developed because the state-of-the-art RDBMS systems of that age could not scale to the
needs of the Googles/Yahoos/Facebooks during the phenomenal growth spurt of the early Web. The novelty here was the tradeoffs they made to scale out and up using the compute and storage footprints available at the time.
"We thought of that" vs "we built it and made it work".
"We thought of that" vs "we built it and made it work".