Hmmm... no devices attached and now it is there under Calibre | Library Maintenance. I guess that had to have been the reason (guess it makes sense you can't maintain your librry with a device connected but i sure wish Kovid would have chosen to simply gray the entry out rather than make it disappear!)
Since you're so helpful, where would I find calibredb? (not that I need it now, but I
would like to know for future reference.
A Spotlight search and a peek into the apps folder don't show it, and unless you're in the proper directory, terminal mode won't run it either!