Magpie source is hosted on Github, because it's open source - it's public. There is no requirement that the git repo you use to store your data be on Github. The git repo for Magpie and the git repo for the data you access through Magpie are not intended to be the same.
Part of it is motivation. Why bother leaving, if I don't have a particular destination in mind? There are other things I could be doing that seem more important.
The other part is that I fall into patterns really easily. If I don't have a set destination in mind when I leave my apartment, I often just end up at the subway stop I take to get to work.
I'm terrible at walking w/o a destination in mind. A while ago I made this crappy little web tool to give me a random destination to meander to: http://roust.sknkwrks.net/