For a page that has a billion users and is a prime spoofing target, they probably have real data showing that any visual adaptation results in substantial user confusion.
If any visual adaptation results in substantial user confusion, then why roll out this update which they say is "strictly a change in visual appearance"? If they're going to cause confusion, at least incorporate some additional functionality at the same time.
> If they're going to cause confusion, at least incorporate some additional functionality at the same time.
That seems like the worst time to add new functionality.
When a service is being redesigned, I hope improvements to the functionality is what's leading those changes. Causing confusion without any benefits beyond a "more modern look" isn't the best reasoning for a redesign.