Why some Hosted Games can't be bought off Steam?

[Jacic]

As others have already said, it’s a valve issue. Most HG’s and a number of COGs are not on steam at the moment. You can read about it here:

Will you be adding more of Your Games to Steam?

Firstly, is there a reason you can’t purchase the games on the main website? Or in the chrome store? (Those are the two alternative options if you’ve PC and not a tablet.) Here’s what Dan has to say.