I browsed the Terminal "man" files for Security and Keychain and like missing preference files, when a keychain is not found a new empty keychain will be automatically created. These commands come to MacOS from BSD Unix via Apple's Darwin that is at the core of all Apple's current operating systems. While I was unable to trace the entire login sequence and determine what the precursor commands would be I am guessing that being unable to open a keychain because it is damaged or the password is unknown might count as "not found". While that would explain your empty keychains the question of what has changed to trigger this condition and why remains unanswered.

🤷‍♂️



"All you've got to do is own up to your ignorance
honestly, and you'll find people who are eager to
fill your head with information"
--Walt Disney