Every non-beta site's FAQ is styled to match the permanent look and feel of the site for which it was made. Why don't they have specialized screenshots as well?
Because it would be a waste of time.
Oh, there'd be some small benefit from it, no doubt. Always helps to see a screenshot that looks exactly like what you see on your own screen.
But it would also mean that every change to the design, on any of the sites, whether a massive re-work or a small bug-fix, would require remaking those screenshots.
Either design changes would be held up, or they'd be perpetually out of date anyway.
Much better to just use images taken from the default theme, which are already designed to be as clean and universally appealing as possible.