It is not entirely clear why these moves on the US government wallet and the transfer of Bitcoin to a new wallet are happening, but most likely the reason is not selling, at least there is no official statement.
One of the analyses of these moves might be that this is just a political move by the old President Biden after Trump's statement about the reserve, maybe he wants to tell him that I am still in the White House and you do not own anything, also perhaps some senators who oppose Bitcoin want to sell the government's Bitcoin before Trump takes office.