The X-Men have always lived in an especially fantastic corner of the Marvel Universe. From resurrection to time travel and hopping across dimensions, the X-Men have made wild concepts like these a cornerstone of their world for decades. But now that Krakoa is the center of the X-Men's world, some of those concepts aren't entirely welcomed on the mutants' new island nation.
One of Krakoa's secret founders, Moira MacTaggert, imposed a hidden rule that forbids the resurrection of mutants who can see the future. Moira's mutant ability to live through entire lifetimes before being born again gave her information that was vital in shaping Krakoa's future, but the existence of mutants with the ability to tell the future threatened her designs for mutantkind. However, mutant precogs aren't the only X-Men who have a good idea of the future. The X-Men know several time-travelers from other future timelines, but none of them have gone through Krakoa's resurrection process yet.
For the moment, it does not seem like there is a complete ban on time-travelers from being part of Krakoa as a whole. Cable, Rachel Grey and Bishop all hail from alternate futures, and they've all been in storylines that have centered before on their ability to change the past and redirect the trajectory of time. That's precisely the kind of thing Moira has worried about precogs doing since a conversation in a previous life with the precog Destiny, who explicitly threatened Moira if the secret mutant were to interfere with Destiny's own designs.
The explanation could simply be that the specific alternate futures of those X-Men don't interfere or crisscross with Moira's plans at all, but there's also a more sinister possibility lurking in the horizon. It could well be that they simply haven't interfered with her machinations just yet, and it's notable that none of them have been resurrected through the miraculous process honed by Xavier and the Five.
While the relative prominence of those X-Men could also play a role in their continued presence, several less prominent X-Men who've spent time in the Marvel Universe still haven't been revived. To name a few, Bishop's sister Shard, Cable's son Genesis, Trevor Fitzroy, Nate Grey, Nemesis and Dark Beast all have yet to be revived, even though they all had a presence in the main Marvel Universe.
Since Bishop already plays an active role on Krakoa, it's not clear what trouble could come from reviving Shard and Fitzroy, who also hail from his home reality. However, the potential lack of characters from the Age of Apocalypse timeline is especially curious. Omega-Level mutants are widely considered Krakoa's most valuable resource, which the absence of the ultra-powerful Nate Grey -- who vanished at the end of the Age of X-Man crossover -- particularly puzzling.
In theory, some of those dead mutants could have simply perished before Xavier had the chance to copy their consciousness with Cerebro, but that still doesn't explain everything. Shard, Nate Grey and Dark Beast all spent enough time around the X-Men that their consciousnesses had to have been backed-up by Cerebro at one point or another.
While all of this could merely be coincidence and happenstance, the lack of mutant resurrections is eye-raising at the very least. It also raises the question of whether time-travelers like Cable, Bishop and Rachel Grey would even be resurrected if they perished.
While there are still some questions about whether or not Moira has any real reasons for the ban on bringing back precognitive mutants beyond her own resentment towards Destiny, very little revealed about her endgame plans has been revealed since the end of House of X and Powers of X. At any rate, Moira and Xavier have a tight grip on the future of mutantkind on Krakoa, and it doesn't seem like they'll give that up any time soon.