exactly, it is what the market currently wants.
Hardly. Customers are not stupid, People do not play games they do not like. You can easily see games that are a bust, big numbers at the start which quickly tail off. Civ 6 numbers have been rising steadily since launch.
https://steamcharts.com/app/289070
and Steam numbers do not cover games played on consoles or phones.
The PC games market has totally changed over the past 20 years, tastes have changed, the market is younger, there is more appetite for casual games, PCs now only account for a small part of the market share, most consumers play games on consoles or phones.
Businesses have had to make a choice, either go for the mass market with products with a broad appeal or become niche players with a product marketed to a more hard core crowd. Civ has become a casual strategy game with nice graphics and a bit of action that you can play on basically any device. Perfect for the player who wants to be entertained for an hour with something not too difficult when they have some downtime. The owners have found the winning formula which is very profitable for them and their shareholders. They are not about to change it and you can expect any future expansion pack or new game to be more or less along the same line.
Now players can of course complain that Civ 6 is not the hard core, ultra realistic strategy game of their dreams, but that is not the game the Devs are producing and you are not their market.
So yes, the Civ series is "doomed" to follow the same formula and continue making lots of money for Take-Two and its shareholders.