You misunderstand how markets work. Before it was much easier to manipulate Bitcoin's market by smaller parties and bigger parties. Now the number of parties that can manipulate it is shrinking and it will continue to shrink down to a few hands. In the last phase there will be nobody left who can have a big impact on it, but for that the market cap needs to grow a lot more.
The problem is that since the irruption of the "strategic reserve" idea, there are entities which could potentially acquire millions of BTC. Even if it's unlikely that a single nation will really buy > 2-3 millions of BTC on its own, several nations together could form a cartel with certain common interests. FATF for example is an organism made up by a lot of governments, and if all FATF member states together had let's say 20% of the Bitcoin supply, then it could have enough power to reject privacy improvements which require softforks.
This wouldn't be a single manipulation event. It would be constant pressure on developers, exchanges and miners to reject privacy-related softforks. Normally, users have the option of an "user activated fork" as a last resort in this case: forking away from the main chain implementing the update anyway without miner consent. But the "FATF cartel" could scare users to use this pro-privacy Bitcoin fork, selling millions of coins on this chain to impose the chain with less privacy.
This "manipulation threat" is limited to certain issues like privacy where such cartels could form, of course.