I doubt Cable factors much into this at all. Just a gut feeling, but with Hickman commenting about what a mess X-men continuity is, he probably doesn’t want pretty much the worst offender in that regard front and center for his big magnum opus. When trying to take the concept in a bold new direction, you don’t want to be saddled with a character so emblematic of a specific period in the past. Same reason why Morrison didn’t use him, or Rachel Grey, and really only used 90s and 00s characters very sparingly (Bishop and Sage briefly in one arc).