While that makes sense for working people and before high school, it doesn't explain the situation for university students. Time in university is rather stress

While that makes sense for working people and before high school, it doesn't explain the situation for university students. Time in university is rather stress free for the majority of Japanese students. Another issue with your assessment is that things have gotten better rather than worse in terms of personal time and freedom. Still worse than in other countries I'm sure, but the trend there does not correspond with the dating trend. My impression is that people who do have free time in Japan spend an awful lot of it on their hobbies and doing additional part time to fuel them, where hobbies are mostly travelling, media consumption, or going to events (like live concerts). There' no shortage of consumers who spend time and money on entertainment. Also, I'm not sure the article says anything about dating in general. It talks about both (!) some people not being interested in sex and others being more intetested and earlier. Things are getting more extreme on both ends. I don't think that is explained by stress or work and academic pressure. I don't have an explanation but maybe it's grounded in the fact that people have more (!) personal freedom then less these days, i.e. that there is less pressure to go along with what everybody does. As far as I know that is not too dissimilar to the situation in the 70s so it kind of makes sense.