This is an absolutely amazing 1st world country with 3rd world construction practices. I blame it on several factors:
1. Cheap and scammy construction companies that try to maximize their profit margin by using cheap materials and poor building practices.
2. People who don't know any better. Most Japanese people assume that what they get is standard and fair.
3. The pervasive Japanese mindset that everything is disposable, replaceable and ephemeral. In Japan, little value is generally placed on long term value of things.
The house where I grew up in Europe is built like a castle compared to even some of the best houses I've seen here.
If this doesn't sound crazy enough, there are a lot of carbon monoxide related deaths every winter in Japan because many people (especially elderly people) use an ancient heating system called /kotatsu/, where they burn coal under a small table that's covered with a blanket. My girlfriend once got burnt badly because she fell asleep under her kotatsu and accidentally touched the heater. Don't get me started on electric blankets and similar nonsense, which is all over the place.