Because that would leave ABrowser unmaintained, and thus open to security and
compatibility problems.
Australis is terrible, of course... so why not have CTR included by default
as part of Trisquel? Trisquel is already noted for having a "non-default"
GNOME layout when first installed, so why not have a "non-default" browser UI
as well?
And, if a user doesn't like the way the "new" ABrowser UI looks, CTR will
allow them to customise it right away, without needing to install the add-on
themselves.
