For the younger generations, I think it's a little more complex than being obsessed with work and tech.
For those that grew up in the bubble years, a large number of men seem to be looking for someone to take their mother's role. Someone who will be home when they get back from work, have dinner ready, the house clean, kids in bed and a hot bath ready - the stereotypical 50s housewife in American terms. More and more Japanese women don't want this - they want a career and to be on equal terms with their husbands. They also face little to no financial pressure to marry since a large portion of single Japanese people live rent free with their parents until marriage, so they have a rather large disposable income to do what they would like, either alone or with friends.
For the "millennial" Japanese, they have many of the same problems that generation sees in America - a lack of jobs. Japanese companies have moved away from the lifetime employment that used to be the norm, and more and more jobs are contract or part-time work. Especially for young men, there is an enormous amount of pressure to get a full-time company job like their father has, and when they can't meet this expectation there is a tendency to withdraw socially.
Combine both of these with the a culture that's still fairly bound in tradition and hasn't really accepted women's rights as a whole, and it's not really that surprising that women aren't just jumping to give up their careers to get married and have kids.
With that being said, most Japanese people still want to get married (somewhat older survey, admittedly), and Japanese people are having sex.
Japanese people definitely aren't having children, but this is more of a developed country problem than a Japanese problem. If you look at birth rate by country, Japan is one of the lowest, but depending on which data set you look at, Germany is lower, and that's with a much higher immigration rate that should help that figure go up. However, no one seems fixated on the idea that Germans aren't having sex.
Look at fertility rate by country. Per the CIA Factbook, South Korea is at 1.25 to Japan's 1.42, but no one seems focused on the end of South Korea as we know it.
Wacky Japan sells; panty vending machines, hikikomori, rabbits on leashes - we've built up an image of this weird place that is so different than what we're used to, and it's easy to type up a quick story on a slow news day. The truth is, it's not so different than anywhere else in the west if we weren't allowing a fair amount of immigration.