A major problem is that they don't think the same way that we do and that their goals are completely different.
We seek to learn what we can of the real world, whereas they simply want to disprove evolution. Hence such things as evidence and methods of measurement (including dating methods) have importance for us. None of those things are important to creationists, except for how they might be able to use or misuse them or just plain lie about them as a way to disprove evolution -- or at least to cause the unwary to question or doubt evolution and any science that they wish to discredit. We seek to form an integrated understanding of the world, one that is
self-consistent, such that everything needs to be enough in agreement or at least not directly contradict each other; eg, physics must agree with astronomy and with chemisty and with biology, etc. They do not seek any such integrated understanding and are quite happy to hold several contradictory positions, just so long as it contradicts evolution and the findings of science that they disagree with.
Here's the case in point where I finally realized that. On a Yahoo forum, a young-earth creationist presented the old PRATT about the amount of sodium in the oceans limiting the age of the oceans to millions of years. Along with educating him on residence times, I asked him why he was trying to argue that the oceans are millions of years when his position is that the earth cannot be any older than 10,000 years. His response was, quoting from memory: "I'm perfectly happy with the oceans only being millions of years old, just so long as they're not
billions of years old like sciences says!" That's when the light-bulb went on in my head: they don't care about forming any kind of self-consistent world-view;
they only want to disprove evolution (and any other science that gets in their way).
Edited by dwise1, : corrected a couple typos