I’m curious, what hypothetical scenario do you imagine where Apple got any real world benefit from having files appear above Dropbox when searching for “dropbox”?
Setting aside whether Files is a competitor (which I’m honestly not sure it is) I would imagine that at least 99% of the time, a person searching for a specific product by name isn’t in a mind space to be conquered by a competitor.
You asked for a hypothetical scenario so I'll give you one. User starts using Files instead of Dropbox to view their file that are stored in the cloud on Dropbox.
Apple wants to drive up iCloud usage so they add a one time prompt into their Files app asking if users want to upgrade their iCloud storage. It's not a massive deal on it's own but this would take users away from Dropbox and Dropbox has no recourse to convince the user otherwise because users are accessing Dropbox through Files (since that's the #1 ranked app they downloaded instead of Dropbox).
Setting aside whether Files is a competitor (which I’m honestly not sure it is) I would imagine that at least 99% of the time, a person searching for a specific product by name isn’t in a mind space to be conquered by a competitor.