Civilization VII attempted a revolutionary overhaul to the traditional Civ system. Instead of one long game, you could play through three separate Ages. Instead of having a leader married to their Civ, you could have them swap out depending on the Age they're in. A lot of those changes sounded really interesting, but at launch fans decided they preferred the more traditional style of play.
Take-Two CEO Strauss Zelnick said that Firaxis always tries to push the boat out for a new Civilization game, but this time it didn't land, and he takes full responsibility. "Every time there's a new Civ, the team at Firaxis thinks about: 'How do we push the envelope far enough that it makes sense to buy this new game? And how do we preserve what people love enough so that they're not disaffected?' And we got it wrong with Civ VII, but it wasn't for want of trying. And again, I take responsibility for it," he said in an interview with Game File.
Zelnick said that Civilization is still a "profitable enterprise" for Take-Two, so it seems fans shouldn't worry about Civilization VII being the last one or anything like that. Civilization VI also was panned at launch, and is now one of the most popular games in the franchise. Civilization VII might have a tougher job winning people over with its key gameplay changes, but there will always be fans hoping for its triumphant comeback.