One reason surely is that it's Japan's one legal outlet for gambling, allowing players to try their luck and win money playing pachinko. In fact, during Japan's long economic downturn many turned to pachinko in a last ditch effort to make ends meet.
Pachinko are popular gambling machines in Japan; what people don't know is that most of the pachinko parlors were owned by Koreans as their main form of business when they migrated to Japan. It is not a coincidence for Pachinko to be the title of the series and the main setting for the show's opening.
