Only since 5e did it become clear to me that a single adventure book, like Curse of Strahd for example, was considered a full campaign and the expected end of for these characters. Perhaps we never played (A)D&D as intended…
Aside from Slavers -> Giants -> Drow -> Demonweb, Temple of Elemental Evil, and some other odd bits, the phenomenon really derives from when Paizo published Dungeon and Dragon magazines with Adventure Paths.






