The way Japanese houses are made, it is cheaper to rebuild than to refurbish.

The most expensive part of a Japanese house is the concrete foundation, and this is reused sometimes. The rest of the house is just cheap wood and plastic (yes, many times, the exterior wall is just plastic that imitates bricks or stone).

Also, the new houses are build according to the updated anti-seismic regulations so, obviously, people always prefer living there.