So, it looks like the Baby-Sitters Club series gets a little weird towards the end.
First, there's a character shuffle. Dawn is kicked out of the series, to make room for a new baby-sitter named Abby. Jessi and Mallory narrate books about half as often as usual, until they just sort of stop narrating altogether.
Then, there's a shift towards more mature storylines, like child abuse, Claudia being sent back a grade, Stacey's boyfriend getting depression and Kristy going "too far" with her boyfriend. The series ends with Mary Anne's house being burned to the ground.
They had a sequel series called "Friends Forever", where things seem to mostly calm down and get back to normal, except one with a kidnapping mystery. For whatever reason, Ann Martin still used ghostwriters the whole time (with two exceptions). I wonder why the attempts to get people interested in the series again did NOT involve having the original author write more books.
The weird part? The spin-off Baby-Sitters Club series seemed to be doing fine. Little Sister and California Diaries kept trucking along, well past the cancellation of the main series. The Baby-Sitters Club mystery series ended shortly before the main Baby-Sitters Club series, but I'm not sure if that's due to poor sales, or because the one ghostwriter (Ellen Miles) got sick of writing them.
In the end, it was decided that all Baby-Sitters Club related books would stop production, in 2000. That's around the same time Animorphs got cancelled. I remember people blaming Harry Potter for the cancellation of long-running children's series, because it was such a huge cash cow that Scholastic didn't need any other serials, especially serials that looked outdated. Other long-running children's series--Nancy Drew, Sweet Valley High--got the boot around 2003-5.