The remote-helper bridges to access data stored in Mercurial and
Bazaar are maintained outside the git.git tree in the repositories
of their primary author:

    https://github.com/felipec/git-remote-hg (for Mercurial)
    https://github.com/felipec/git-remote-bzr (for Bazaar)

They were unbundled because the maintainer thought it was best, without
actually giving an expalantion. The closest thing to an explanatioin is [1],
which was refuted.

However, the lack of quality was not in question, in fact, they can be
considered as "graduated".

For more details ask the Git maintainer.

[1] http://article.gmane.org/gmane.comp.version-control.git/248951