Why not open source it? It's code that runs on my phone, not on their servers. I have no reason to download an app that could just be a well designed web site. It being closed source makes me very suspicious of it. What does GitHub have to hide? It's not like the app is some breakthrough innovation.
...I mean that is true of a lot of apps on the App Store right now, I don't think developers are under any impression that they have to make every app open source.
True. This is why I don't install any apps. And you would think a company who's business model revolves around open source would be more likely to open source their app.
Does their business model revolve around open source? It seems to be the opposite. I don't have to pay anything to host open-source repositories. We get free repos now too, with caveats though.
I think an analogous questions would be, Does Google's ad business revolve around search? I expect most would say yes. They don't make any direct money off of organic links, but those are what drive millions of eyeballs to their ads every day.
Being the go-to place for open source code is what leads a lot of people/companies to GitHub's paid offerings.