My understanding is that the number of people signed up is in the thousands, which if it is correct means probably a bit less than one in a million persons. You might have meant it rhetorically, but if it is true that it is a "big mystery" to you why most people have not signed up, then your best guess for the reason for this should be that signing up for cryonics is foolish and useless, just as if a patient in a psychological ward finds himself thinking, "I wonder why so few people say they are Napoleon?", his best guess should be that the reason for this is that the people he knows, including himself, are not in fact Napoleon. As another example, if you are at the airport and you see two lines while you are checking in, a very long one and a very short one, and you say, "It's a big mystery to me why so many people are going in that long line instead of the short one," then you'd better get in that long line, because if you get in the short one, you are going to find yourself kicked out of it. On the other hand if you do know the reasons, you may be able to get in the short line. In the cryonics case, this is pretty much true no matter how convincing you find your reasons, until you can understand why people do not sign up.

Are those two 10% figures equal only by coincidence? To me, "boost membership by 10% above trend" means either "increase this year's signups by 10% of what they would otherwise have been" or else "increase this year's signups enough to make membership a year from now 10% higher than it otherwise would have been". The second of these is equivalent to "membership will be 10% higher a year from now" iff membership would otherwise have been exactly unaltered over the year, which would mean that signups are a negligibly small fraction of current membership. The first is equivalent to "membership will be 10% higher a year from now" iff m+1.1s = 1.1m where m,s are current membership and baseline signups for the next year, which is true iff m = 11s. Those are both rather specific conditions, and the first seems pretty unlikely. Did you actually mean either of them, or have I misunderstood?