The current Shaman King fanbase basically caps out around 150,000. Yes, Flowers and Zero get initial prints of up to 65,000. Then maybe push another 10,000 sales over the following week (bringing it to 75,000 in a 2 week period). Doubling that number is the total fanbase (for everyone else who bought it after that 2 week window). The challenge is bringing that number up the next 50,000.
The big difference between SK and PoT, DGM, and TLR is they went from one series right into SQ. Shaman King has the hurdle of missing out on KZB and Flowers. It's hard to get new fans (or bring back old ones) into a series where you need to say "go buy these 32 volumes, then 2 more, then 6 more, then maybe 2 more if you want, then you are caught up!" Yes, Remix sales (with 2 prints) were good to help bring people back up to speed but then you still need to get them to read Flowers. With the other series you can "get by" with the anime and then pick up a couple manga volumes (within the same series) to make the jump. With Shaman King, you need to commit to 8 to 20 volumes depending on where you left off.
Starting Flowers up again from where it left off isn't easy, since there has been alot of things started. Yet another "break" in the story might be good. It's not an easy transition back in from any point.
And creative control probably plays a big part in what Takei does. One of the least-liked arcs in SK? Golem arc or "Epilogue" where the editor was pushing Takei towards ending the series. Then flip it around, few people like the original Jyuki Ningen Jumbor series, and he probably had too much control. For Flowers, he's spent basically a year on the "Death Zero" arc. If you are in a "competitive manga magazine" that's a huge risk to say "I'm going to leave the plot of the manga and focus on 3 characters for the next year." That takes alot of creative control, and I find it unlikely Editors to say "yes" to that, unless you really don't have anything to lose. Like the magazine ending. Luckily he's gained alot of respect with his peers, which I'm sure helps alot.
(Ok, the Death Zero arc probably was planned for like 5 chapters at most, but Takei got a bit too much "into it.")
Another interesting thing about Takei is that he normally only releases 11 chapters a year (for monthly magazines). But page count wise, he's closer to 10 chapters (with a chapter split into 2 19-pages). So it's assumed he contracts with the magazine on a yearly-page count. When his time was up in SQ for Ultimo, going to SQ19 was just a change in the contract to half the number of pages. Would SQ basically exempt Takei for having 11 chapters being printed without any chance of being cancelled? What if Flowers basically turns into Ultimo, does SQ want to take that risk? It's hard to say.
Plus, Takei has been making the bold moves to leave Shueisha and be more of a "free agent." It makes it a bit more competetive, but it's hard to say if that's really going to pay off. I'm sure he's happy with Hyper Dash Yonkuro, but he's got some more work to get Shaman King back again.
