Well that is because I really want to have full control of the group. I myself look around for work, which I then myself add to the group if I feel it fits. If I make a contribute button/make it possible to contribute, I will be spammed with all kinds of crap not related to the groups content. This happened to the last 2 groups I had, which I pretty much gave up on. Now, because of that, I disabled the contribute button, and add things myself.