In a traditional datacenter the cost of increasing the scale of computing environment is much higher than a Cloud computing environment. Also in a traditional data center, there are not much benefits of scaling down the operation when demand decreases. Since most of the expenditure is in capital spent of buying servers etc., scaling down just saves power cost, which is very less compared to other fixed costs.
Also in a Cloud environment there is no need to higher a large number of operations staff to maintain the datacenter. Cloud provider takes care of maintaining and upgrading the resources in Cloud environment.
With a traditional datacenter, people cost is very high since we have to hire a large number of technical operation people for in-house datacenter.Read the full book at www.amazon.com