Well, the fan-made mockup has such look because that's the only thing you can do with the screenshot.

Real mod could do much more, e.g. changing textures or models geometries.

It's the whole new cartoony art direction that's weird and off-putting, unfortunately evoking the feel of cheap mobile games.

Here is a real world photo example of what look modern AAA "Civ-like" game could strive for:

http://i.imgur.com/p4XZDeR.jpg

It's possible to be lush and colorful, yet realistic and more mature looking.