Except for the secrecy of Colossus, Crypto AG, the 9/11 hijackings, Bill Cosby drugging and raping dozens of women, Peter Thiel funding lawsuits against Gawker, the Manhattan Project, the CIA-funded coup against Mossadegh, Stuxnet, the Five Families, most of what the NSA does, the Stealth Bomber, and so on.
Almost all of those remained secret longer than the 17 years we're talking about here, and due to selection bias, I am forced to omit the much more successfully kept secrets, because I don't know about them yet.
The selection bias, is discounting the endless conspiracies exposed daily.
People go to jail, are caught out, fired, relationships break up, governments fall, because conspiracies of even a few people fall apart. It's a regular thing.
You're mentioning some things, of which some were known during the time. The FBI had reports of the 9/11 hijackers, Bill Cosby was known by many but the women were paid off with cash or jobs (until they rightfully went public), and things such as the CIA and the Manhattan project are laced with highly patriotic people, and the death penalty or life in jail, along with people sequestered and watched by immense security.
Secrets are very difficult to keep.
The things you think of were enormously unusual in that they were kept.
Very plausibly the identity of Satoshi is already known to more people than Cosby's rapes or the 9/11 hijacking plans, before everybody knew about them. The hijacking plans weren't even well-known inside the FBI! And it's also very plausible that the people involved in Bitcoin were either strongly idealistic, facing death penalties for disclosure (for example, if they work for the Mossad), or both.
I agree with your weakened claim that secrets are very difficult to keep, but much of modern society is built on institutions that are very good at keeping them: armies, intelligence agencies, and even companies with trade secrets.
I agree that Satoshi was probably just one or two people, and the difficulty in keeping secrets with more than a few people is one of my reasons for that. But you said it was impossible, not difficult, which is much too extreme to be justifiable.
(I think it's about 50% likely that it's one of a couple of dozen people I've met personally, but I wouldn't be able to convince anyone else. So you might be talking to one of the people in the position of Bill Cosby's friends before the news came out.)
I agree with your weakened claim that secrets are very difficult to keep
I think the mindspace here is what I was taught. A shared secret is no longer that. That the more people which know, the more impossible it will be.
As humans, we must conceptualize different sides of the problem, differently. As a person attempting to maintain secrecy, the impossible nature must be kept in mind at all times.
This is doubly true with some personality types, which think everything is a game. I've often wondered if some people feel mental pain, when held to their word.
So framing is important.
But from the other side, one can point to exceptions to the rule.
Almost all of those remained secret longer than the 17 years we're talking about here, and due to selection bias, I am forced to omit the much more successfully kept secrets, because I don't know about them yet.