I think there are multiple reasons why the share of gamers playing strategy games may not be as high. The "mainstream-ization" of games is one. If we turn the clock back to the 1980s, people who played strategy board games or wargames were a natural early audience for the new video game industry. Why did Avalon Hill develop a video game adaptation of
Advanced Civilization? Because there was a good likelihood that someone who played board games or war games a couple nights a week with other people might be interested in playing one at home on some of the other nights as well. So, early on, strategy was a key genre.
Now, games are quite mainstream, and many people are playing them who don't have that background. I think there is also a blurry line - is
Stardew Valley a strategy game? It has management aspects. Whether you report yourself as playing strategy games when you play games on the blurry line likely varies.
The "lack of blockbuster games" theory also makes sense to me. And while we like to focus on 4X games here, I think RTS is if anything a bigger impact on the (potential) declining trend. We used to have Age of Empires, Warcraft, Starcraft, Rise of Nations, and so many other big RTS games that drew in lots of players. Lately, we have Company of Heroes III, and... They Are Billions and Northgard a few years ago in the larger-scale indie arena. I'm sure I'm overlooking one of two, but they are a lot less prominent than they once were.
I liken it to why I haven't been going to the movies - I like action movies, but not superhero movies, and it seemed like every film released in the 2010s was a superhero movie, with almost no non-superhero action films, so I stopped paying attention to what new movies were being released or going to theater, except the James Bond films that were mainstream enough that I still knew when they were arriving. It's the equivalent of someone who used to play a lot of strategy and RTS who has only bought
Civilization VI over the past decade, because everything else was under their radar (and I've since learned that there were a few good action films in the 2010s, and am looking forward to one or two new ones this summer as that industry finally starts making a variety of films again).
Lowering attention spans? Maybe. But I agree with Hygro, One More Turn keeps attention spans long, sometimes dangerously so. I could see an impact there in people being less willing to start something with a reputation for taking a long time nowadays - that's the primary reason I never tried World of Warcraft, and part of why I haven't joined a D&D group - but I suspect the impact is low for existing players. Still, if the pie has grown and more of the newcomers want quick-and-short games... it would add up.
The "life is more stressful, people want to be relaxed rather than challenged" idea... I'm more skeptical. Sure, sometimes it's nice to relax by playing some
Rocket League, but it was nice to relax by playing some
Chivalry in 2013 as well. What was better than One More Turn for forgetting about the pandemic for an evening? I could see
Hearts of Iron feeling a bit too close to home in the last two years given Russia's war of aggression, though I'll give it credit for helping me understand at a more practical level the importance of reliable supplies of, say, artillery shells. But the trend in the IGN article predates that, and there are plenty of strategy games with other themes.