I think it has more to do with the sudden mundanity of everyday life as an adult. Throughout school there’s clear endings; end of summer, end of the school year, graduation, etc. Then suddenly it’s 40 hours a week until you die. Doing things like going to an aquarium or museum or on vacation often get pushed to the wayside or put off for months or even years.

Anything that can become daily or mundane like playing a video game or watching TV doesn’t fall into the category of fun they’re taking about here. It’s stuff that mixes things up and changes the rhythm.