@Rain Spectre
That's not true, people
do care about mangakas, same as game directors or movie directors, especially when they have a style which in the case of most mangakas they have a distinct storytelling style and art style.
E.g. when you go see a Tarantino film you expect it to be violent and stylish, people that read Stephen King's books also expect a certain writing style (So much that when he tried to make books, Hideo Kojima too with Death Stranding for example.
Sure, it's not like authors can always create successful hits, and sure authors won't probably always make the same kind of movie/game/manga, some do, like for example Masami Kurumada always making battle shonen manga, Nobuyuki Fukumoto creating betting manga or Naoki Urasawa creating Mystery manga (Though I think some of his earlier works weren't thrillers?) but there are also mangaka (and every other kind of creators) that move from the genre that first established them, e.g. Takehiko Inoue doing Slam Dunk and then Vagabond, Akira Toriyama moving from gag to battle manga with Dr. Slump to Dragon Ball.
There's probably a good reason that Samurai 8 has been picked by various publishers around the world (I think it's already being published in some, with only 3 in Japan) same with Eden's Zero and IIRC Rinne when first launched back in like 2009 was published digitally at the same time in the US iirc, it was all because fans wanted to support a work made by their favorite author.
I'm not saying an audience will just blindly buy/watch anything new an author releases, that's just not how things work, but there certainly is a fan base that's dedicated enough and will follow everything an author makes, or at least be interested in his/her new work. Perhaps with super popular titles like Naruto or One Piece only a "small" fraction of fans will buy everything published by Kishimoto or Oda, but you can bet they will at least give it a try just because they want to see if their favorite author came up with a cool new franchise.
For other more "niche" authors (Think authors like Kohji Kumeta, Suehiro Maruo, Nobuyuki Fukumoto, authors with a very... stylized approach to their mangas) their fans are more fans of the authors than their manga, like they would probably read anything made by the author. (Kinda like how Junji Ito is being published right now in the US and globally, as anthologist of horror stories and stuff, because fans don't really care about one particular title, sure Uzumaki probably sold more than the anthologies but most fans buy the manga because it's a Junji Ito manga0