Most organizations get started by creating an application or two in the public cloud. With it's high level of data security and the ability to copy your data locally, anytime you need it, many organizations never need to go any further.
On the other hand, an organization might want an On-Premise Installation, for a variety of reasons.
Applications created in the cloud can be packaged into a zip file and added to an installed version of the platform, wherever it may be. So nothing is lost by starting in the cloud.