There is a single sufficient "good reason" to fork a project. You want to. People are free to use your fork or ignore it.
What have the forkers contributed to the product so far? Where are the technical reasons for the fork? Where is the community discussion and consensus? Has there been any kind of democratic action? So on what basis is the word 'community' used?
A fork shoud not simply be about people misusing the word 'community' for seeking control and ownership because that's not what open source is about, is it?
A lot of the forkers and go-gitea group members wrote essential features for Gogs and contributed thousands of lines of code. They simply got impatient waiting sometimes 3 months for their PRs to get merged. Especially bkcsoft did tremendous work on Gogs. As a contributor to Gogs that stopped contributing because whose last PR wasn't merged for a very long time, I welcome Gitea's idea of a faster development schedule.