Board Thread:The Quarters (Q & A)/@comment-78.199.240.204-20140204084846/@comment-24185151-20140211105245

I believe it is because the aim of habit is to encourage a person to *earn* these items rather than receive them as gifts. It extends the so-called "sweet spot" of gameplay in which the game is an effective incentive to do unpleasant tasks. The longer it takes to complete a collection, the longer it is that you are encouraged to continue playing. :)

At least that's the idea.