Sim City 2013 was a brand new engine, and only shipped on PCs. It probably needs more optimization to run as well as it can, while still meeting the demands of the game. Even though it may seem simple, the vast variety of buildings provides challenges in the texture part of the engine. It's possible that an average GPU lacks enough memory to hold all the textures at once during parts of gameplay, and texture swapping slows performance greatly. It's sometimes one of the pains of developing a sandbox game, players can create some very performance taxing situations.

Call of Duty is usually reusing the previous years engines with a few more features added in. Odds are that codebase has had a long line of optimizations applied. CoD is also focused on consoles first, where they have to meet certain performance and quality metrics enforced by Sony/Microsoft/Nintendo. Porting it to PC is still a bit of work, but it also tends to bring over many of the optimizations. Textures in particular are going to be heavily optimized to fit into console RAM space and be able to be streamed off a slow optical disc. CoD is also not a sandbox game, so the scope of what needs to be run is always known ahead of time, allowing further optimizations. Lots of subtle tricks in map designs can hide loading times as players run along very specifically designed paths.