I find it interesting that his goals for 2015 seem to be focused on selling his courseware, etc. on optimization, etc.
This is where the Tim Ferris comment comes from...
He claims to have spent only a handful of hours on BCC last year. So spending less than say 20 hours on a project and having it generate ~30% of revenue, passively, seems like a pretty good deal.
Another poster mentioned focus, but that doesn't really seem to be the case here.
Of course all this is conjecture.
[1] http://www.kalzumeus.com/2014/12/22/kalzumeus-software-year-...
"Focus" is a very valid reason. Even assuming just one hour per week, that's 52 hours he can spend on something else. Plus having BCC around is a mental burden. Even while you're not working actively on it, you're thinking about it.
[1] http://www.kalzumeus.com/2015/05/01/talking-about-money/