Future expansions.

If the developers included a huge number of characters, units, and Castles (8, for example) in each game in the series, whether it's the 3rd, 5th, or 6th installment, then no matter what the plot was or how the graphics were done, and even with the distribution of powers and magic among classes, instead of having everything the same for everyone, as in the 6th game, then everyone would love this pseudo-series of games. People like massiveness and variety, but what do the developers do? They create an initial version with limited resources, abilities, Castles, and units, and then, to prevent the game from "dying down" in the eyes of its fans, they develop expansions. This raises the question: why can't they just create the expansions together with the game and then visualize the game, adding small but effective "features"? Apparently, this is a financial aspect that we don't understand.