> An upload button alone is no user story, a story might be "As a user, I want to be able to import the Excel reports that I get from company $XY, so that I don't have to manually enter the data, and save a lot of time that way", ideally including a reason why that data needs to be there.
The implementation of this functionality in a way that will delight customers could hypothetically take 3 weeks as it requires the implementation of an upload button, a datastore to store the uploaded values, and an integration into a legacy feeds system to get the spreadsheet's data to all of the places it needs to go.
In most scrum processes 3 weeks of effort would not be accepted, and the story would be "broken down" into smaller issues such as "implement an upload button". Even worse scrum projects emphasize anti-patterns of "parallelizing" efforts, so we'll assign each of those smaller stories to separate individuals. While theoretically a customer focused engineer could look at the original user story, there is minimal incentive to do this - and most engineers will focus on pushing stories across the board, the upload button may or may not ever work in a way that customer's desired - and any attempt to fix it requires restarting the whole process.