Just because it sells "millions" (it does not) now, what makes you think it will continue selling "millions" for years to come? All businesses, no matter what service they provide, make sales projections. Based on sales trends, they project long and short term sales estimates. If long term trends indicate declining sales, coupled with declining customer feedback, then projections will indicate waning popularity. Bleach's sales are down about 30% since Aizen was defeated. In the same time Bleach went from a regular in the top five to a regular in the bottom five. Both would indicate a strong decline in popularity. It should be obvious, but Jump does not tolerate any series spending to many weeks in the bottom five. Obviously a series as old as Bleach will be given more time than Pajama or Kurogane. But there is little chance Kubo can continue Bleach indefinitely. This arc will be the last, as promised, and it will end in a reasonable amount of time. This arc will not last as long as the Arrancar arc. Nor will Kubo be given as much time as Kishi has had to complete Naruto, a much more popular manga.