Небо
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You can check the statistics on Steam. For example, Paradox games, which you mentioned, are regularly updated and supported: Stellaris has 10,667 players, and Crusader Kings has 13,481. Or, if you look at the strategy games section on Steam, Age of Empires IV has 7,280 players. Then, take a single-player game like The Witcher 3: 12,829 players (and people also play these games on consoles, unlike strategy games). Civilization has a decent 38,000 players. I don't even compare it to games like Dota and Warcraft.
You can make money from strategy games; otherwise, they wouldn't be made at all. But it's not as easy as with other games. It's not just about the publishers; even the players themselves don't want to pay for the development of a good game that they have to wait several years for.