Homes and condo buildings in Japan aren't supposed to last more than 40 years. It's supposed to keep the national economy in a constant state of development (sort of good) but it also means most people can't make a good long term investment off home ownership (which is bad). Either way, yeah, there's no incentive to renovate, because they won't be up for too long. On top of that, a lot of them need to be refurnished or rebuilt to be quake-proof, but it's not affordable, so they may opt to wait until the next big one brings it down.