Why are write permissions required?

I just ran into an issue where I was unable to run a migration from a CSV file deployed via Git to an Acquia cloud server.
This was due to file permission issues.

I discovered that this is due to the migrate_source_csv module requiring write access mode for the csv file.

https://git.drupalcode.org/project/migrate_source_csv/blob/8.x-3.x/src/P...

return Reader::createFromStream(fopen($this->configuration['path'], 'r+'));

My question here is, why is write permission required? When would we ever want to modify the file? Is there a reason we cannot use 'r' (as this would work fine on Acquia).

Thanks