You are correct, Google trends is pretty much irrelevant here. You would be surprised by Gitosis (and many others you've dismissed). It's pretty much in every company I've worked in over the last 7 years. It's never well liked, but it works just fine. Most companies don't need bells and whistles that come with GUI based git installs, so they don't waste the money switching away to them.
If course Google Trends is not equal to installed base. But based on our experience I also don't think gitosis still has a massive installed base.