Why weren't Kingdom Heart volumes released regularly? Why did Kingdom Hearts manga series release new volumes so far apart from each other?

The game has been out for a long time, so the plot is pretty much predictable.

Plus, why have they stopped KH2 in the middle, and begin with KH358/2?
Initially, the publications of English volumes weren't that far apart; the English Kingdom Hearts and Chain of Memories were on a release cycle around 90 days.



However, that changed in 2008, when TOKYOPOP, the English publisher, underwent a major corporate restructuring. Many of their projects, including Kingdom Hearts translations, were delayed following the first Kingdom Hearts II release. This effectively slowed the English releases of Kingdom Hearts II to a halt.

In addition, Shiro Amano (the artist) went on hiatus from Kingdom Hearts II after volume 2 in favor of Kingdom Hearts 358/2 Days, so Japanese versions stopped after volume 2 as well. (I don't believe Amano or the producers had any comment on why he did this.)

Kingdom Hearts 358/2 Days has been completed with 5 volumes, but shortly after Tokyopop's reorganization was finished, they lost the majority of their licenses and effectively shut down, which halted the English Kingdom Hearts series. Thus, those English volumes never saw the light of day.

On a side note: Recently, Yen Press announced that they had purchased the rights to the Kingdom Hearts series. They will be re-releasing some of the old volumes first, then:


  Yen will kick things off with the first volume of the fourth series, "Kingdom Hearts 365/2[sic] days" in November, and it will release the four-volume "Kingdom Hearts" series as two omnibus volumes (dubbed "Kingdom Hearts Final Mix") in May 2013 and the two-volume "Kingdom Hearts: Chain of Memories" as a single omnibus in June 2014.