The reason why the Kansai-style eel restaurants existed was that the artisans and cooks, who came to Edo because of Sankinkotai (a system under which feudal lords during the Edo period were required to spend every other year residing in Edo), settled in Edo, and began their trade.
関西風の鰻屋が存在した理由は参勤交代で江戸までお供した職人や料理人がそのまま江戸に定住しそこで商いを始めたとされる。