Most creationists argue that nature has been clearly designed, and therefore there must be a designer.
What is really happening here is that they are mistaking emergent behavior for design.
Emergence is the appearance of complex patterns from the interaction of simple rules. This can be seen all the time both in nature and in artificial situations (such as in some computer games.) Surprisingly complex behavior can result from the interaction between surprisingly simple rules. The outward appearance of the complex behavior might look a lot like it has a purpose and design, but when we actually study the underlying phenomena and rules behind it we discover that there actually is no purposeful design, that the overall complex behavior has just naturally emerged without any actual guiding hand.
It's very hard for the human mind to fully comprehend emergent behavior because it's a quite complex subject. Therefore people make the mistake all the time, and see patterns and design where in reality there are none. On top of that, creationists in particular are extremely biased and have an agenda to try to "prove" that the design is there. Because of this strong bias, they will refuse to even try to understand the true cause of the apparent design.