And then you setup the forward rendering pipeline, and the programmable shaders, and the skeletal animation system, then the inverse kinematics for procedural a

And then you setup the forward rendering pipeline, and the programmable shaders, and the skeletal animation system, then the inverse kinematics for procedural animation, then the asset pipeline for publishing to different platforms, then the netcode, then the realtime physics system. Did I forget about reflection probes? How about a terrain editor? Maybe you need to bake lighting to make your game look good. I think this comment might wildly underestimate just how much modern game engines like Unity, Godot, and Unreal bring to the table. They may very well be the most complex pieces of software in the world today