I don't remember the US government buying bitcoin, ever! Or am I missing something?
Nope you didn’t.
The bitcoin the USA holds is not through purchases but from cybercrimes. They most likely don’t care whether bitcoin goes up or not. They are not holding it for profit or as an investment opportunity but they are holding it because of legal causes.
People should learn how to differentiate holding for profit and just seizing it from “criminals”. USA’s stance on bitcoin or crypto at large remains pretty much the same.