It’s not a modicum of ethics, it’s ass-covering in the case of legal challenges from the countries where these items were looted. After several high-profile antiquities cases in the early 90s and 2000s, and a federal precedent out of New York, every museum was forced to do this kind of bare minimum due diligence to avoid prosecution. Prior to this, they were being brazenly in bed with organized criminal networks in buying this stuff.