Part of it’s because Yakuza 1 had waaaaay less side stuff to do than 2 and up, so they added a lot of things to this from Zero. But I don’t mind locations being reused across games in Kamurocho proper just because it’s not like the games take place centuries apart and also because many of the locations are actual places like the Mondrian themed nightclub in 2.
But part of it also is these games aren’t really mean to be played immediately one after the other. Even these most recent two which use the same engine, were released a year apart in Japan. I wouldn’t blame anyone for getting bored of the locations if they played them one after the other.
Despite it’s age, even going from this to the upcoming Yakuza 2 remake you’ll see a massive difference in the scope and length of the story, but still see plenty of familiar places and faces.