Stellaris is popular because it's in the vein of simplified 4x instead of a complicated sim, and thematically sci-fi has wider appeal than non-WW2 history.It's flashy, makes big promises and has the company that made EU4 and CK2 behind it. By the time you realize it's an unspired, shallow mess you already played 100 hours and bought all the DLC. But it still has enough potential to keep you trapped in a state of "maybe this DLC/big overhaul patch will finally fix everything" and you just get strung along. Fuck, I typed all this and I'm still hopeful for the 2.2 overhaul and consider getting Megacorp.
Here's some :autism:- I've had this sense for awhile whenever I'd look at the Paradox subreddit or whatever, the way people talked about these games made me feel they didn't actually play them. Especially when it came to CK2, always repeating the same memes. It goes beyond tired jokes. People have nothing other to say. Looking at Steam statistics today, I think I'm right. CK2 has an average total playtime is 33 hours... and the median total playtime is 4.5 hours. So you've got some people who do play it a ton and skews the average, while most finish the tutorial and try to take over Ireland. Vic2 is very similar.
Stellaris is surprisingly ahead though. Average total playtime is 76 hours, while the median total is 27.4 (and remember this is total and CK2 is four years older). HOI4 comes in at 136.7 total average, 43.8 median. EU4 has a respectable 200 total average, and median of 23.5. CIV 5, as a mainstream point of reference, has 95.2 average total playtime and 33.5 hour median.
I'm not arguing Stellaris is good, just that people like this type of bad and Paradox knows it.