Evolution provides a mechanism for describing how the world got to be the way it is today. This allows evolution to explain phenomena in our world. Why do some species look more alike than others? Evolution claims that they are related phylogenetically. Creationism, as far as I know, makes no attempt to explain this basic trend, and many others. Why did God make creatures that look alike, or better yet, make creatures that have large amounts of DNA in common?
This is the defining feature of a scientific theory- employing a mechanism for explanation of data. Creationism is mostly composed of arguments against evolution- irreducible complexity, etc. Yet these arguments are simply against ToE, not arguments for another scientific theory. Saying that "God made it" is not an explanation, please explain where, when, and how did he make it? Why did his act of creation lead to cerain trends, like the inter-relatedness of species? Evolution simply cannot scientifically be replaced by Creationism until Creationism has a theory which can explain the why the world is as it is today.
On further point about the displacement of scientific theories- in many cases, a new scientific theory does not completely throw out an old one. For example, General Relativity did not throw out Newtonian physics. Rather, a major point that lead to the acceptance of general relativity was its confirmation of Newtonian laws for slow-moving objects in a fixed reference frame. In other words, the new theory was only accepted after it proved the old theory to be true in the cases that we commonly use the old theory for. This is not always the case, but describes many of the "revisions" to science in the last 200 years.
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