That is interesting!I haven't had a series fail yet, but the sales are influencing me. My first series and the one that's got the most books is a thriller/suspense. It sells okay, and I make well more than I spent on them, but they are dwarfed by the later two series (in immediate sales. The first book in my first series has sold the most books, but that's partly just because it's been out so long)
I wrote the first book in my second series and put it out in the summer, and it sold multiple times better than any of the thrillers, so I was starting to think when I finished up that series I might do 2 Romances (it's not really a romance, it's closer to a coming of age, but the Amazon tends to lump it together).
I didn't think my newest series would do great, because it's a smaller genre sales wise than Romance as well, but I managed to get in the best sellers, which made it become my best performing book out of the gate.
So I am thinking about other series and several stand alone stories, and taking the sales of the three I have into account before I decide what to do. If a series flopped I'd probably do 1 more to draw it to a conclusion, so that I didn't have something completely unsatisfying out there for the people that follow and buy all my stuff, but I probably wouldn't continue it past that.
If you ever want to write up your numbers/experiences/advice in the SP subforum, I'm sure I'm not the only person who'd be grateful