This is because, in and after the bubble economy era, the price of land in large cities rose steeply, and many came to live in the suburbs from where they could commute to their offices or schools if using Shinkansen (mostly in Tochigi Prefecture, Gunma Prefecture and the east part of Shizuoka Prefecture for commuting to offices or schools in Tokyo).
これは、いわゆるバブル景気以降の大都市における地価の高騰で、新幹線で通勤・通学が可能な郊外（主に東京への通勤・通学を目的に栃木県、群馬県、静岡県東部が多い）の住宅に住む人が増えたためである。