They need to sell volumes in order for Shueisha to make money. The mangaka today do not know how to sell volumes. Don't let anyone tell you 30K is as good as it gets or is in any way acceptable. I enjoy Hinomaru and Samon kun, but they need to get out of the magazine. They can go to Jump Plus or MiracleJump or Jump GigaCroossed-2 but mangaka have to know that if they sell 30K that their days in Jump are numbered. Quite frankly, it's embarrassing.
Sure, but after so many long runners ended this year, they already have 5 brand new series less than 6 months old (and an empty spot that has yet to be filled from Red Sprite ending plus another spot when Gintama ends in a few months). Neverland has secured it's place, but who knows how long it will take for the other 4 to be filled. At least 2 of those are guaranteed to be failures already, Demons Plan and Ole Golazo are still up in the air, at least one will probably fail. So out of the 7 series that have started in the last 6 months, we have 1 likely success, and 2 low maybes.
Canning the 30k sellers would empty up another 5 spots, meaning 10, soon to be 11 of the 20 or so places in the magazine are essentially empty. It's taken 4-5 months for Neverland, a series that's been pretty hyped and popular from the beginning to finally be of worth to the magazine. In addition, each new series is generally a 3 month investment minimum, even if it's an axe job. I hardly think they're in a position to empty up 11 spots in the magazine when 5 is hard enough to deal with. Especially when you consider they're lucky for 1/3 of series at best to be keepers, and even then the likely hood of them selling well is even lower. It will take like 2 years+ just to fill the places they have vacant now, they don't want to be doubling that... Don't you think this is exactly why they haven't canned them?