It's an interesting theory, but still of the reasons was just a theory at any argument, there are still a lot of questions that can break these points anyway, so it doesn't prove anything, mostly just a theory.
US might have the time and opportunity but so as other countries and one individual as well.
I get that, but I would argue that only the US government is big enough to ignore $80 billion. For any other government, except perhaps China, it would simply be too much money to withhold from the people.
I doubt that Satoshi couldn't be anonymous from the government, there are a lot of ways to do it. Satoshi might be dead, or he never intended for this project to be like this when he created it, that is probably why he never able to spent a single sat on his wallet. I don't understand why being dead doesn't explain anything why he never spend a single sat.
Being dead is an explanation, but the counter evidence here is that he explicitly said goodbye before he left the scene. That would detract from the theory that he died suddenly before he was able to spend his sats.
At this point, most of these arguments don't matter anymore since Bitcoin has already built a huge foundation, and there will be nothing that can easily break that, as long as it continue to be what it is today as a investment and a digital currency, then most of the investors is not going to complain about anything, because it is doing its own job, even though it wasn't maybe made for it in the first place.
I agree that the US government being the inventor of Bitcoin doesn't fundamentally change Bitcoin. There is the issue of the disposition of Satoshi's 1M coins, which, if this were to come out publicly, would make their sale a political issue, and thus affect the price of BTC.
However, one thing you can see just by reading this thread is that many people believe a lot of false things about Bitcoin and have a rather ridiculous notion about how the US government works--but they believe that stuff because it creates a mystique around Bitcoin that drives them to purchase more of it. Finding out that Bitcoin was just another skunkworks project within the US government will kill that illusion once and for all. And those disillusioned people might be a significant part of the BTC buying pool and those that would weigh negatively on the price.
So I don't agree that it would make "no difference". You can debate the exact amount though (and it's hard to predict).
I will believe you said this based on what you are also willing to know, but who are the jobless people who spent millions searching for Satoshi when they should have spent that money helping people who actually need it?
There have been many journalists, and they even made a movie out of the question. I don't think those people are... jobless. Quite the contrary, they have made a good living trying to find Satoshi, which is based on very significant demand for this question to be answered.
Trillions of dollars are spent each year on things that are more trivial than this. Humans love their entertainment after all.

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If the US government really created Bitcoin and it is still under their control, then this is bad news for every investor.
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Satoshi being a person or group within the US government would not change the control of today's Bitcoin in any way.
I have argued elsewhere that the US government can, if it wanted to, deeply affect the market price of Bitcoin, which is all most people care about with Bitcoin. And because of that, the US government could, if it wanted to, completely change Bitcoin's architecture (say centralized) by holding the price hostage.
And the US government already exerts enormous control over Bitcoin because of the control of the on/off-ramps, securities laws around exchanges and brokers, and direct control of the Bitcoin ETFs traded on its stock exchanges.
But "Satoshi" does not control Bitcoin, so it doesn't matter who/what he is.