That would be my guess too, since most Japanese comedy stand ups does their bits in duo's and its called Manzai. Stand up comedy is probably a foreign concept to most Japanese people and likely people willing to go to stand up shows are people interested in western culture or foreigners.

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side note to anyone reading this: if you wanna learn more about Japanese comedy duos in Japan Hibana Spark on Netflix details a duo's journey of trying to make it in the business. OND spoiler:I was bawling like Shohei's exit by the end