Comment by nine_k

Rewiring an entire country is a wee bit expensive. Even if the wires are rated to 300V (they usually are), transformers would have to be replaced, and they cost quite a bit. Also different sockets and circuit breakers, and a whole lot of billable hours by licensed electricians.

(But changing the voltage is easy compared to changing the mains frequency. Japan still has to live with 50Hz in one half of the country, and 60Hz in the other.)