Personally I think it is because it has terrible performance. Scenes that Unreal seems to be able to render at full frame rates run at a fraction of that in Unity. Even its vaunted 2D system is slow as balls... load times for Graveyard Keeper, as an example, are agonizingly long. And for what? A hundred megabytes at most of 2D pixel-art assets? What is the engine doing with all that time? Certainly not just loading and decompressing shit into RAM.
Reminds me of the unnecessarily long GTA Online loading times that were a result of parsing a giant JSON file. Is it really worth blaming the engine when maybe its the game doing something improper?
