Why so Little Air in Japanese University Student Bicycle Tyres?

I was waiting for the lights to change at the main entrance to my university, when I noticed that almost all of the rear bicycles tyres of the students waiting at the lights were very low on air. They are in danger of having "pinch flats."

It was only the rear tyres that were almost flat. Could it be that rear tyres are out of sight and therefore out of the Japanese mind? Or is that bicycles in general -- almost always of the step through, shopper or in Japanese parlance "mama" variety -- are given short thrift in Japanese culture, and to take care of ones bike is a rather nerdy thing to do? Or was it just a coincidence, and in general Japanese students' bicycle tyres are no less inflated than those of any other nation?