360 vs 383

A good question to discuss might be why in 1971-2 the factory engineers decided to drop the 383 in favor of the 400 and while turning it into a gas-guzzling pig (in stock form) or conversely, why was the 340 similarly replaced with a lower-performing but larger displacement engine?
Probably due customer demand for mid displacement engines 350-400 cid in the 70's.