Parkinson's work expansion is very often on the form of new features, better finishing, higher quality, and etc.
It doesn't necessarily imply people creating bureaucracy out of thin air to justify their existence. It's just means that people don't leave extra time being "extra".
The busy-work explanation isn't even consistent, because people mostly can't create busy-work in a project scope. It's something that comes from the overall processes.
Possibly we're taking by each other. Persons with a focus on a narrow work goal, when given extra time, will probably come up with extra, productive goals using that extra time. It's not bureaucracy (at least for the honest), and it's not busy-work. It's just better work; but, it's outside the parameters of the originally defined task. Often, they'll ask the tool to help them. Not for the piece-work element, but for a slightly expanded purpose; maybe simply for organizational goals that aren't in any handbook. Sometimes it's vanity, sometimes it's lulz; it just seems pretty human.