One interpretation is that sushi shops in Edo, as a result of the invention of nigiri-zushi, completely shifted their attention from the Kansai-area style sushi such as oshi-zushi (lightly-pressed piece of sushi topped with cooked ingredients) to nigiri-zushi.
ひとつは握りずしを創案し、それまで押しずしなど、上方風のすしが中心だった江戸市中のすし屋が、握りずし一色に一変したという解釈。