There are two factors at play here.
First, and most importantly, model editing software is designed to make editing the model easy, and not to render hundreds of things at once. As such it may use more complex/slower data-structures and algorithms to store and display the model, if it helps with the editing.
The second thing is that games often use lower quality assets (for performance reasons). It is quite common to edit a model in super high quality (simply because it’s easier that way) and then create a much faster version to use in game. The in-game version could for example use normal maps instead of polygons for small surface details, compressed textures and coordinates as well as baked AO or lighting.
Latest Answers