Not enough people read any more! Books were the original singleplayer, narrative-focused experience. But for every one kid who read, there were always ten who were outside kicking a ball around (I jknow because I was that one who read).

Same thing in games, given that the gaming audience is still relatively young. For kids, getting together online with your mates and and showing your skills is a lot more rewarding than working your way through a challenging narrative on your own.

Also, as in books, there are your formulaic paperback 'originals' (Darksiders, God of War), your mainstream popular tales (Mass Effect) and challenging 'literature' (Elden Ring). All requiring a slightly different mindset and skillset to play. You can button-bash your way through the linear tales of Darksiders or the original God of War trilogy with only decent reflexes and a thirst for destruction. Mass Effect, however, requires rather more thought and attention to possible consequences. Don't get me started on Elden Ring! I will finish it, one day!

There will always be a lesser demand for these challenging games, just as the demand for complex literature is less than it is for pulp. But there will always be demand and more so as the demographic ages and older people become less self-conscious about continuing to game.