It was because Kaisho was a place where people of lower status, such as Doboshu, could attend the games of renga and Tocha (Tea Gambling where the player had to guess the tea brand) and share the same space.
それは、身分の低い、例えば同朋衆が、連歌や闘茶などの遊びの際に同席して、同じ空間を共有できる場として、会所があったからである。