Except now they have an additional "season pass" for nearly the same cost of the game for what used to be included for free.
I've seen that on Reddit as well, you think companies have a year worth of content and holding onto it ... The content is just not ready / created.
Black ops 4 had one for $40[1]. Can't seem to find historical info about civ6, but I know a "large expansion" was not included in the season pass.
[0]: https://ew.com/article/2016/02/17/fallout-4-season-pass-pric...
[1]: https://www.polygon.com/2018/6/13/17447600/call-of-duty-blac...