Nodevember is offering refunds, so it's very hard to see how this could be a scam, and difficult to imagine how Nodevember would stand to make anything but a large loss by removing Crockford as a speaker. They chose to proceed with this anyway, which is indicative of serious concerns.
Removing him as a speaker and remaining quiet about the exact reasons can mean any number of things.
Suppose they have compelling reasons to believe having him speak would be harmful, but that they do not have a firm enough basis that they are comfortable publicising, in which case publishing their rationale could be both unethical itself and could expose them to legal action.
Or perhaps they have received information in confidence, from sources they trust, but believe that information received in confidence is not theirs to publish without consent. Or perhaps their information is alarming and yet primarily circumstantial from a constellation of different sources.
In essence, there is a fairly wide terrain where it is perfectly warranted to have deal-breaking levels of concern about a prospective speaker without being in a position to merit publishing accusations against them.
From the responses here, it seems that many struggle to imagine conference organizers could be placed in such a position. This is exactly kind of bias we might expect to find in an overly white and male subculture where navigating these kinds of murky waters is at most a purely hypothetical exercise rather than a day-to-day reality.