Icheb was killed off gruesomely. Intiraymi would've been far better than Casey King, even though I guess it was a flashback to nine years after Voyager and 13 years before Picard, necessitating a young adult Icheb and not one in his forties. But Intiraymi should've been fine in a short role with a proper wig and makeup to hide any age discrepancy. I think he probably balked at the idea, and they went with someone else. Still Intiraymi was a major, multi-season recurring actor, with major plotlines and entire episodes devoted to his character. A big difference over the recasting of Maddox.
It causes me worry over who they might recast next. Naomi? Harry Kim? The Outrageous Okona? They spoiled us with Jonathan Del Arco.
I would assume the recasting has more to do with Intiraymi's social media comments from a couple years ago. Specifically the ones mocking people who had come out because of the #metoo movement, including his mocking of Anthony Rapp.