Simply put, there is a lot less of a use for Fox movies in Comcast. Universal already makes big movies, like Jurassic World and Fate of the Furious, and they make small ones like Blockers and Get Out with regularity. While Foxs X-Men properties would give Universal a superhero franchise if they so desire one, the upscale flicks (The Revenant comes to mind) might be in peril. Universal doesnt distribute super-duper expensive flicks outside of the FF and JW franchises. More importantly, Im not sure a single studio would need both Girl on the Train and Gone Girl.
Blue Sky would be less valuable to a studio that already has Illumination and DreamWorks Animation under its umbrella. Blue Sky may get sold no matter who buys Fox (Lionsgate might want to take a gander), but Fox Searchlight would be a hell of a lot safer at a studio that didnt already have Focus Features pumping out the likes of The Darkest Hour, Tully and Victoria and Abdul. Having Focus Features and Fox Searchlight doesnt buy Comcast anything it doesnt already have. Hence the types of movies that Fox and Fox Searchlight produce might become an endangered species.