First it was the Affero General Public License that Google banned from its Google Code site, an open-source code hosting site. Google contended that it didn't want to encourage license proliferation by accepting projects using licenses that don't have widespread use and acceptance.
This week, however, Google nixed a highly popular, important license license: Mozilla Public License.
Google's Chris DiBona played the proliferation card again against the MPL, but also admitted that how Google determines whether a license is suitably popular is "so arbitrary." Great. That makes me feel better. At least there's a clear criterion for deciding. Not.
While some projects have moved away from the MPL in recent years, it remains one open source's standard licenses. I've got to think this has more to do with MPL derivatives (It's no secret that DiBona disliked the "badgeware" licenses that derived from the MPL) and their potential impact on Google's ability to consume their code, just as with the Affero GPL, than with any respect for license proliferation.
If it were about proliferation, Google would settle on GPL/LGPL, BSD/Apache, and MPL. Between those, most licensing preferences would be covered. By leaving out the MPL, however, Google has mistakenly dumped the baby with the bath water.