Thanks for the detailed reply! My suspicions were that it may have been related to the complexity of manufacturing (including the materials development that’s enabled it within the past several decades), but the costs alongside that had slipped my mind given the scientific reasons that would have been more of a hard block in the past.
Also across the various replies here, TIL a bunch more about what’s up with PEX, which I’d not gotten around to researching. Sounds like some wicked stuff all things considering!