Same reasons that pertain to the Easter Bunny: there's no physical evidence that such a designer exists.
"Same reasons that pertain to the Easter Bunny: there's no physical evidence that such a designer exists."
It appears that this is the crux of the matter. Scientists claim that no physical evidence that exists that can support the claim that a Creator exists. Creationists and IDers use the argument that the orderliness and complexity of the PHYSICAL universe IS evidence. Some scientists don't accept that as valid evidence so in their minds, no evidence has been presented.
ID claims that it is more rational for the bacterial flagellum to have been designed than evolved. The evidence is presents includes irreducible complexity.that parts can't reduced without destroying function; specified complexity, that the DNA which makes the flagellum work is complex and specified hence no scientific mechanism can account for it; and the inference of design, that the design of a event can be inferred if it meets certain objective criteria.
Now, where is the physical evidence that it evolved?