“The nail that stand out is hammered down in japan. We do not want the unique house with lots of character… The tile is in case the homeless or drunk man pee on your house, it is easy to clean like the bathroom. Japan is convenience country.”
From the ever hilarious Ask Kazuhide, although many a true word said in jest (at least in the first part).
My other theories:
The necessary earthquake proofing has cut down on the number of suppliers and the number of models they can offer, and hence leaving people with little choice but to pick from the crap designs they offer??
The fall in land prices has meant formerly posh areas have got much more mixed, breaking up the rows of cool and/ or odd bubble year houses with lower middle class grey boxes