I think that's a good question from a technical and analytical standpoint. The technical reason why Sherlock went through with it might have been an excuse just to incorperate the scene, and that makes me wonder about the significance of the scene. It was very emotional and exposed a lot about their relationship, but that was kind of negated when we saw the death was staged. Whether it was designed to send us reeling into theories, idk. I didn't spend too much time doing that as there are prently of creative and reasonable explanations for what happened. What I got out of that scene was the feeling of empathy for both characters in that moment. I dare say I might have even been satisfied if Sherlock had ended there.
