User blog comment:MisterWoodhouse/Social Activity, the 2010 Editor, and Unpausing Migrations/@comment-33265265-20201005024914/@comment-24258073-20201005025818

Because they've chosen to use Wiki-style forums on that wiki. Based on my usergroup permission tests, any user can edit that namespace on UCP, regardless of wiki settings. Last time I checked, it is possible to use both Wiki-style forums and Discussions on UCP at the same time.