While Bazaar was promising in its early days, the open-source distribution revision control system has seen better times. The original developer of Bazaar, Martin Pool, left Canonical last year and the company ended up shuffeling around the other developers formerly working on the project. Bazaar isn't a money-maker for Canonical and the control system in its current form is good enough for the company while most other free software projects prefer Git or even SVN over Bzr.
Bazaar 2.6 was originally talked about for release in August of 2012, but that never happened. The most recent release of Bazaar is version 2.6 Beta 2, which happened in July of last year and came four months after the first beta. It's now been over seven months without another development release, the official 2.6 release, or any Bazaar 2.5 point release.
When looking at the Bazaar repository for Bazaar, there's just been a single commit in 2013, which was just a bug-fix release. The last time there was more than a single commit in one month's time during 2012 was in October, while since then the project has been at a standstill without Bazaar 2.6. Based upon activity around it, Bazaar seems basically in a limited maintenance mode now as just a tool for building Ubuntu that's under the control of Canonical.
Bazaar has received contributions in the past from outside developers and is considered to be a GNU Project, but GNU projects don't mean much nor a lot of development activity even for "high priority" GNU work.
Those wanting to dig around some more can visit bazaar.canonical.com.
Update: Another point is that there are currently 212 high-importance bugs and 2081 open bugs against the Bazaar software.