9/11 pierced America's sense of safety. Perhaps Pearl Harbor was similar. Historically the Gauls sacking Rome in the 4th Century BCE was probably similar. So people were attracted to media where somebody would save them, protect them.
At a higher level, the superhero genre feeds into pushing an idealism narrative. Idealism here simply means some people are the good guys and other people are the bad guys. Inherently. Compare this to materialism, which is a philosophy that there is a feedback loop between a person and their environment, of each affecting the other. There is no good or evil. People simply respond to their circumstances. A Song of Ice and Fire (the books more than the TV show, particularly the later seasons) is a superb example of materialism in fiction.
So what does the rising popularity of Japanese literature (note: the article is about that and not about anime as I think some who simply read the headline assume) say about society?
I think we have a crisis of despair in society. The cost of living, particularly housing, is out of control. You have a generation who thinks they'll never own a home or ever be able to retire. They don't feel like they have the security to have children. Is it any wonder that escapism thrives when the real world seems so bleak?
I see this as yet another symptom of the crisis in capitalism. Sure there's a fascination with Japanese culture. This isn't new. But why? We're also seeing more Chinese fiction (eg Three Body Problem). It's hard for me not to see this trend as anything other than a failure in our society to provide hope to people whose dreams are very mundane.