One of the many reasons Cloud solutions are so attractive is because of the substantially lower capital investment costs to implement them, when compared to building your own solution. Many vendors are willing to give away equipment & services initially, knowing full well that once you're in their ecosystem they'll get their money back, tenfold. How can they be so confident? Well, generally because it'll cost far more than your agency can ever afford up front in order to leave their ecosystem/solution. That's their business model.