People who are both highly intelligent and have high conscientiousness are capable of perceiving many variables simultaneously and abstract them into refined simplified solutions. People with lower intelligence and high conscientiousness are still capable of perceiving these variables but will struggle more to put them together in a meaningful way necessary to achieve a polished result. It should be noted that conscientiousness is negatively correlated to intelligence at around -0.24 - 0.27, which is a big gap that explains why some lower intelligent people are unexpectedly more capable of high quality delivery than much higher intelligent peers.
People with low conscientiousness cannot refine complex qualities into simplified output. The cost is just too high irrespective of their intelligence. The result is sloppy output that just costs less to start over every time than to refine or extend. This will appear that these people tend to preference complexity, and in a manner of speaking that isn't completely wrong. It's not so much that they prefer complexity but that they are just incapable of expending the effort to build more meaningful systems.