Real Computer Graphic engineer here. I am, as most of my co-workers are, very anti-Unity. First reason is horrible default shader it has, that you can spot from a mile away. Any light calculations are way longer that they should be, unless you polished it very hard for what you are doing, or made a new shader that does not suck. Make no mistake, it sucks, no arguments or doubts. Second is it can have some problems with some other programs, at least compared to Unreal you mentioned. And third, its actually slower to develop than in Unreal. Now, I’m not saying Unreal is always better, but it is in 70% of the time. HOWEVER, Snapshot games choose Unity for a reason. Maybe they are better/more experienced at it, maybe they got better deal for licence or maybe they have some specific implementations in mind that would not work in Unreal. Probably all three, if I had to guess. As for the 3rd reason of the 3rd reason, you must remember that game engines are not tool, they are skeletons and internal organs. The skin you put on is, well, a skin deep.