The entire concept of how the files app works and integrates indirectly with everything on iOS is effectively a stand-in replacement--maybe a better one for some use cases, for sure, but that seems besides the point--to Dropbox. This is because iOS ostensibly doesn't really want to have a file system, and so the concept of storing things into the Files app--which is the interface for and is largely backed by iCloud Drive, which is 100% a competitor to Dropbox--is about as weirdly indirect as storing something into Dropbox. I would thereby think that, in fact, a number of people looking for Dropbox's functionality--to share files between apps on their phone and store them in the cloud--might get tempted to use Files instead to accomplish that exact same core use case.