To be able to present a case before the US Supreme Court, one thing that you need is "standing". Fine, I can see that any Joe on the street is not going to be able to be heard. In like manner, experts in their field are not interested in debating just anyone who has a challenge. Nor do creationists need to "debate" evolutionists whose only notable characteristics are irrationality and rage.
So, why does Richard Dawkins refuse to debate William Lane Craig? He made all sorts of claims to be willing to debate his topic, then limited himself to high-level religious figures. (Debate a cardinal about science philosophies, sounds legit.) Of course, he debated other people despite the limitations that he set. But he will not debate William Lane Craig. Why not? He certainly does have "standing". Even if he didn't have the status needed, Craig is such a "rock star" in some theological circles (not to me, I have some serious disagreements with him, but never mind about that now), Dawkins can make an exception to his personal rules, debate and shut him up once and for all. But we know that he cannot win, and that is why he keeps running away and making excuses.
Here is a video that is outdated in one respect, but the other eight minutes are valid: