Then let's give you insight to the Harsh Reality that the Game, and its Development Team, are a Failure.
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Of course Stellaris has a different player curve than HoI4! The latter has hardcore history fans willing to play a history-like scenario over and over and over again, while it also has alternate history scenarios meaning the other kind of history fans can play different scenarios. Then it has mods like Kaiserreich giving even more scenarios. Historical context and starting inequality grants a lot of different types of experiences to have in the game. It also has no other modern alternative WW2 grand strategy games.
Stellaris on the other hand must carve their audience out from fans of many different backgrounds, with competition from other 4X space games. It also is partly a 4X game, which always have been less about longevity.
But I think the greatest difference is in how people handle hype. In Stellaris we are all waiting for a total rework of the economy, ressource and planetary system, something relevant for every single empire you make. Every single Stellaris fan I know can't play the game before it comes out. On the other hand Man the Guns doesn't seem to make
that much of a difference unless you're playing with a naval-focus or one of the affected nations, and even then a lot of people are still able to play. I mean I don't even care that much about naval warfare, so I don't feel like I'm missing much when I'm playing.