A quite obvious possibility is that would-be debunkers who want try to go deeper than Penn and Teller style mockery soon realize that they would have to engage much more seriously with cryonics than with Urantia to try to debunk it - sound like they were taking it seriously - implying a far greater loss of status than soaring casually above Urantia, effortlessly trashing it without a hint of sympathy.

"Everyone who's tried to 'debunk' this seems to have ended up writing casual mockery, and oddly enough no would-be skeptics ever seem to engage the arguments in technical detail, and the arguments are being made by people who sure look like they're trying to wear technical hats and include a number of otherwise highly technical figures" seems to me like a quite common position when both of these aspects are combined. There are arguments that skeptics don't bother engaging in detail, but they're not technical. There are physicists who believe crazy things because they're bad outside the laboratory, but then they are usually refuted by more than mockery. I may be prejudiced by being mostly interested only in things that are sensible to start with, but the overall state of affairs I have just described is pretty much what you'd expect a correct but weird-sounding idea to look like.