My suspicion is that he turned Eliezer down because he wants to stick to the standard debate format, where he excels. The few "debates" he lost, particularly the one with Shelly Kagan, were actually informal conversations that closely resemble the sort of exchanges that take place on BloggingHeads.

I like the opening there. Essentially an eloquent and polite elaboration on "I'm at a disadvantage here because it's so obvious to all my peers that this position is right that it's hard for us to even see what the problem is and anticipate what arguments to counter. I mean, for crying it out loud we've been doing it for thousands of years so of course it is possible to do it."