Cue the bereavement model and the diffusion of innovation. Successful advocates of change account for the time and effort it takes to drag people along.
* Nothing about the design was broken before and users don't really complain about it.
* Having used it, the site is noticeably slower. Turns out that shiny is expensive. And I'm on a powerful machine too.
* The UI is now more cluttered and less information dense taking a page straight from FB's playbook. They might be successful but hackers have constantly shit on the design.
* Nobody said that managing a site that large was easy, but doing nothing was always an option for them.
There is a theoretical design that would make the community salivate but this wasn't it.