US law requires what it requires except when it doesn't require it. What you mention is a basically toothless part of the "law", in large part because of other legal restrictions on the functioning of the government and other allowances for lawful penalty-free admission into the US, when it comes to real person US citizens. The OLC/OLA staff for DHS, State and DOJ ought to still know this.

CBP has a routine -- it even publicly indicates part of it -- for US citizens who fly to the US port of entry using an ESTA/VWP country passport and then announce their US citizenship status, whether or not in possession of a current U.S. passport to present, at the US POE. We allow in US citizens daily without a US passport/passport card and do so without fines/incarceration.