But prices don't exist in a vacuum either. The gaming market has exploded and is vastly larger than it was back in 2006.
Steam found games were typically much more profitable when heavily discounted than when full price in general.
How much of content offered is sort of irrelevant. A better metric would be how many gamers buy these things. I'd guess quite a few since they keep going all in on the model (it's getting worse).
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...
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.