Open source development is only a full time paid job for a small number of people, for everyone else it is largely driven by passion. In principal, I'm not sure anyone should tell anyone else what they are allowed to do with their free time.
But if you had taken time to read the first sentence on the link, you would see that there is in fact a key difference:
> Kallithea [...] is [...] source code management system that supports two leading version control systems, Mercurial and Git