The U.S. Government moved its Bitcoin to Coinbase for secure custody and HODL, not to sell.

TL; DR: After a comprehensive process, the U.S. Marshals Service (USMS), a division of the U.S. Department of Justice, selected Coinbase Prime as its partner to safeguard and trade its “Class 1” (large cap) digital assets.

https://www.coinbase.com/blog/u-s-marshals-service-chooses-coinbase-to-safeguard-trade-its-large-cap

Today, the U.S. Marshals Service (USMS), an agency within the U.S. Department of Justice that is responsible for asset forfeiture, announced that it selected Coinbase Prime to provide custody and advanced trading services for the agency’s “Class 1” (large cap) digital assets, which it manages centrally in support of federal law enforcement.

The USMS conducted a competitive due diligence process that evaluated a range of solutions, ultimately choosing Coinbase due to our strong track record and ability to securely provide institutional-grade crypto services at scale.