The difference, is that Dropbox is user-facing software, while Kubernetes is software engineer-facing. Dropbox has to be usable by tech-illterate people. Tech-illiterate people have no idea what a Kubernetes is.

There is value in creating a vertically integrated solution in a space, similar to what Dropbox did, so if you find yourself building many of the pieces of Kubernetes internally, it's worth considering if adopting Kubernetes wouldn't be a more efficient use of resources.