1. CostBig data implies big storage along with enough compute power to go along with the storage. Anyone who has operated an in-house data center knows that setting up and running data center operations is not cheap. One time equipment fees, cost of personnel, monitoring - it all adds up. On the other hand the new pricing framework now put in place by almost all major cloud providers allows the consumers to only pay for what they consume ("pay for what you eat"). Economies of scale that are available to cloud vendors help drive the cost down for the consumers something they can never achieve by themselves.
3. IntegrationHaving your data in the cloud allows you to integrate with many analytics, visualization, and other value added vendors who are also cloud based. In many cases your cloud vendor might already have done some or all of the integration work for you. You can enjoy the benefits of the ecosystem without having to create one.
So, for reasons mentioned above I recommend anyone considering hosting their own data in a captive location to think again.