Always in Wonderland

So, I was checking out the new releases on amazon yesterday and I saw that Jamie McGuire was coming out with another ''Beautiful disaster'' book.

Can someone explain to me why evey new adult book comes with

-A sequel, a companion book from the guy's point of view, 1 or two novellas and when all of these books are released the author writes:

-A new book about the main character's other love interest that didn't get the girl. Then the sequel. Then the companion book from the girl pov. Then, the author writes:

-A new book about the bestfriend of the main character from the first book. Then the sequel, then the companion. Then the author writes:

-A new book about the cousin of the main character, that we saw in the second series about the other's love interest that didn't get thye girl. Then the novellas, and all bla, bla, bla. Then, the author writes:

-A new series about the hotdog seller that we saw for 2 seconds in one of the novellas...

.......

.......

.......

Dear New Adult authors, I love series. I love getting to really know characters and follow them and their lives for many books.

But sometimes, just one book is enough.