not because you disagree with technical decisions, but because you don't like the community management.

Isn't this description every fork ever?

Popular reasons are a disagreement about a license change, or unreasonable barriers on getting things done.

When the community manager (first assumed rogue, but later found to be aligned with Godot's founder) threw a fit and made it clear that anybody who doesn't toil very narrow ideological and political lines is not welcome in the project, there's not much left to do but fork.