Japanese teams play better at home because the crowd is behind them.
Do not bring up the attendance issues for non-home country games in Japan. Japan only has a foreigner population of 1.7 million people (more or less). I am guessing that many of those are working. According to the 2000 Japanese census (ok, it is 10 years ago, but I can find it) the largest foreigner populations were Korean, Chinese and Brazilian and combined at that time it was around 900,000 people. So if this stayed the same, the remaining 800,000 would have to support 20 other teams. This of course does not include tourists to Japan, which would be low in my opinion due to cost of travel and staying in Japan.
If I am working and my team is playing in the town I am working in, I would try to watch. But if my team plays in the 13:00 or 16:00 games, I would be at work (if not on the weekend). Japanese businesses are notoriously bad for not allowing mid-week vacation days.
Tokyo and Osaka are large metropolitan areas and have a decent foreigner population. Hamamatsu is the home of Brazilans in Japan because many work at the auto and motorcycle manufacturers there. Matsumoto in Nagano prefecture is a large city, but the foreigner population there cannot be that big.
Tokyo games always draw well, and I can see that from the attendance figures. Matsumoto did not have a match under 1,000, which is a surprise to me. Osaka's games drew worse than Matsumoto, so this is a bit of shock to me. Osaka had a really good group in my opinion.
Attendance Totals 1st Round
Tokyo 66160, AVG 4411, CAPACITY 12000 (36.75%)
Hamamatsu 26222, AVG 1748, CAPACITY 8000 (21.85%)
Matsumoto 34570, AVG 2305, CAPACITY 7000 (32.93%)
Osaka 19360, AVG 1291, CAPACITY 8200 (15.74%)
It is unrealistic to expect sell outs for all of the games.