Because they're idiots and/or charlatans.
You may call them ignorant, thats fine with me. But I don't think you can dismiss their academic credentials so easily.
Sure I can, since I can identify the elementary, bone-headed errors they make. For example, from your own post:
Examining the science behind the claims of a very old earth using carbon dating techniques
See, there's an idiotic, incompetent comment right there. "Carbon dating techniques" top out at about 40,000 years. Thus they're not used, *can't* be used, to examine or make any conclusions about "a very old Earth". OTHER techniques are used for that.
Only a completely ignorant, clueless creationist could make such a childishly stupid error as that. It's like saying, "Examining the science behind the claims of very distant stars using yardstick techniques"...
You creationists are welcome to come back and try again when you have the first clue, and have a better grasp of science than the average junior-high school student. Unfortunately, that is seldom the case, thus the need for enormously long lists such as this one, detailing the errors and fallacies that creationists keep making time after time after time after time. Read it and weep, it deals with all the classic blunders in your links, and then some.
Just for variety, why don't you guys go get some *new* fallacies for a change? The old ones are getting really stale.
But they don't believe in an old earth. They believe in a young earth, so if you are dealing with 6,000-10,000 years, radiocarbon works just fine. [/creationist mode]
Now if they could just get the results of radiocarbon dating to agree with their claims they might have something!