The Pareto Principle
Other deployment solutions are generic automation/workflow tools that propose to automate every kind of operation in your datacenter, including first-time-installations, database maintenance, and everything else. Obviously, the price to pay for such a a generic solution is that it's extremely difficult to design even basic tasks.
Servantt is focused only in updating existing applications, which obviously is much more frequent than first-time installations, and is exactly the critical activity where you need to avoid errors and reduce downtime.
Since planning a deploy is a piece of cake, developers can focus on what they do best: develop software!