Writing pop fiction or making Marvel movies isn't cheaper than the "artful" variants (in fact for superhero movies it's much more expensive), and consuming isn't cheaper either, so there's more at play here.
For me what makes it popular is the consistency. It's something you eat when you don't want to explore some amazing local cuisine that you may either like or dislike. You just want to get something known.
McDonald's is never amazing but once you've had it you know what every next time is going to be like. And mediocre is better than bad. Also, they really have the fast in fast food licked.
Mentally it costs far less energy to watch a superhero movie than the deeper movies.
I like to watch movies that are for entertainment too, don’t get me wrong. Just want to point out that there is a different in cost to watch different movies, even when the amount of money I pay to watch them is unchanged.