That is why the loyal community are up in arms at the moment that Halo 5 won't support the feature. 343 have now spoken about it by way of a post on Halo Waypoint. Studio head Josh Holmes explained the decision to leave the feature out:
The decision to remove split-screen support from Halo 5: Guardians was one of the most difficult ones we've ever had to make as a studio. We know that for many of our fans, Halo has meant playing together with friends in the same room. We all have great memories of past Halo split-screen multiplayer matches. To move Halo's gameplay forward and deliver a true next-gen experience, tough choices had to be made. Our decision was driven by a desire for scale, fidelity and focus to ensure that we would deliver the best quality experience possible. With Halo 5 we are delivering massive scale environments, improved AI behavior, increased visual and gameplay fidelity… something that truly takes advantage of a new platform. Many of our ambitious goals for Halo 5 would be compromised in a split-screen setting and the time spent optimizing and addressing split-screen-specific issues would take focus from building other parts of the game. Game development is a balancing act of resources, time and technology, and in this case we made the tough decision to sacrifice something that's been near and dear to us all.
I don't doubt the sincerity of this explanation, and I'm sure another part of the game will be better for not having the feature. Will it be the right trade off in the end though and be worth it? Hard to say. We hwill have to wait for the game to see what happens.