It’s almost always people whose lamented busyness is purely self-imposed: work and obligations they’ve taken on voluntarily, classes and activities they’ve “encouraged” their kids to participate in. They’re busy because of their own ambition or drive or anxiety, because they’re addicted to busyness and dread what they might have to face in its absence.
There was another article (which I can't find now) that summarized this even further to state that "I'm so busy" is actually code for "I'm a self-important asshole"... and there's a grain of truth to do this. "Can you help me with X? Can you do Y?" "Oh, I'd love to help, but I'm sooo busy doing other stuff that's more important than you!"