"Branches in git are very lightweight: A branch in git is only a reference to a single commit. With its parental commits, the full branch structure can be constructed." So it takes nothing to have it and gives consistency throughout components. We have to build unchanged components anyway as a step to be sure it still compilable and especially for components in the middle of dependency tree.
Actually all components are changed between releases, but changes not always affects eclipse related code, so it is good to have those changes branched/tagged.