I can't talk for the parent, but in our company, we've made the change hg -> git (using self-hosted bitbucket) and it was quite a costly endeavor time-wise (between testing, configuring and installing BB, converting/moving all the repos, making the changes to our in-house build system, changing all our code signing system (because it wasn't git-compatible) and supporting all the devs who've never used git (or haven't in a long time and forgot everything)), so I can understand not wanting to change what's working.
We use git for all software projects, SVN for all hardware projects. I am not certain about the reasons why hardware department still uses SVN. Probably because every hardware engineer is familiar with SVN and it works for them.