Answer
There are several reasons. Japanese like new one. The price of cars are probably cheapest in the Asia (cos no need to worry importing tax. and other car related taxes are also cheap. Even imported car, like Mercedes and BMW are cheaper than Taiwan and Singapore). And another reason is there is special loan system. It is difficult to explain, but something like this. If the price of a new car is US$40,000, people in the world usually have to pay US$40,000+tax+ other expenses. But some car dealers in Japan deduct "resale price" first. eg. You may be able to sell the car with US$20,000 price in 2 or 3 years later. The dealer deduct this price first, then you can purchase the new car with US$20,000+tax+ expenses only. If you brought the car to the same dealer 2 years later, you can buy new model with 50% price again (real contract is more complex. There are also some risks. But outline is like this). The loan disappear within the years (2 or 3 years). That is why young people can ride new car every a few years..