"Idle hands are the devils workshop" so the old saying goes. I believe Ben was keeping people busy so they would not question his judgement or have time to conspire against him.
The funny thing is, the Others who were overseeing Kate and Sawyer and the anonymous others doing the work, were looking at plans. Perhaps they were continuing the work of Dharma because they believed that what Dharma was striving for was noble, even if the people running Dharma were not.