I thought it was just to frustrate me by pointlessly and annoyingly killing my favorite character every time he pokes his head up.
Spiner should have been recast if he didn't want the gig anymore, Data's life had only begun.
Maybe they can do with him what they do with Dr. Who and "regenerate" him.

yes…because the Discovery folk are well know for being super concerned with visual continuity.
The explanation I've heard for Disco's Klingons is that different races of Klingons exist within the Empire.