Looking at Steam doesn't show people like me, who instinctively disliked the way Civ switching was proposed and have yet to buy Civ 7. Listening to EmotionalHusky narrate his Civ 7 games on YouTube with mixed up leaders and civilizations felt like a stupid joke.
The Devs misunderstand the motives of people regarding their civilizations. Did the Phoenicians settle all around the Mediterranean knowing that their colonies would "flip" to Rome, Spain, Carthage etc? Did Erik the Red go to Greenland expecting it to fail and "flip" to the Inuit? Did the Moroccan conquerors of the Iberian peninsula have sort of a fatalistic attitude that they knew they would "flip" to Spain? Did Champlain claim places in the New World for France knowing that in the future it would "flip" to Britain and later Canada?
Leaders (and their agents) want their countries to persist, so a forced change triggered by an age change feels extremely artificial. It seems like civ switching in 7 has the sort of weirdness of *poof!* aliens replacing everyone in your old civ