If I had to pick two things that have led to adults acting like children, it would be:
- the lack of any real “coming of age” ritual in Western culture. The closest we get is going to college, which has developed into something deliberately removed from adult reality
- the slow removal of cultural rules that indicated a space was to be taken seriously. For example, wearing a suit and caring about your appearance, not using swear words in public, keeping details of your private life to yourself, and so on.
I read somewhere that memes are the artform of the contemporary Zeitgeist, which makes a ton of sense to me. Memes are funny but ultimately just easy, fast-food-style culture. They would not be the predominant art form in a society capable of building something more complex, spiritual, and long-term, like a medieval cathedral or an Italian Renaissance sculpture.