User blog comment:MisterWoodhouse/The first migrations to the Unified Community Platform/@comment-32532-20201021201449/@comment-1807002-20201022163338

I do believe it has been mentioned popular wikis is a factor too. And if it is or isn't not a complex move.

But as a blanket response "larger wikis" may not exclusively mean page count wise it may mean over all content and popularity. But that sounds like what they have been getting at as form as priority.