Because you can't get the look of nuba wax from a synthetic. You can get gloss from a synthetic, but its a hard gloss. It looks like the surface is shelled in with candy. There are a lot of high quality waxes out there right now that last anywhere from 3-12 months. Take a look at Swissvax Shield. A quality wax has a little more depth, more metallic pop depending if its a white or yellow nuba, and a warmer look. It Sometimes I use synthetics on my wheels, headlights, taillights, skirts, and lower portion of rear bumper. For the rest of the car, its almost always a high quality nuba.
2009 E90 328i Monaco Blue
premium/idrive/convience/logic-7/cold weather/ xenons/ saddle brown interior