99% of the time why a series gets axed is because the story simply isn't good.
And that means low ratings and low book sales, which means little revenue for the publisher.
Even if the premise and some of the concepts may be interesting, if the execution sucks then the cool stuff can't save it.
AFAIK Shueisha did try to push for Samurai 8's success, such as having bookstores buy large amounts of Samurai 8 if they wanted to buy other Jump titles, but it still failed to capture the average audience's interest.
Common complaints I know of are exposition dumps, cluttered art, and lack of/rushed character arcs.
Also Naruto's editor in the beginning suggested incredible punches that made early Naruto a powerhouse, like cutting out info dumps, changing Naruto into a human character, inserting Sasuke the rival, inserting the Haku arc, etc.
Maybe SJ gave Kishimoto more creative reins over Samurai 8 that, at the end of the day, didn't work out.