My guess is someone wrote some stupid "Google drive file name FUSE mount" script that attempted to exploit unlimited file storage in metadata. So some team working on Drive ran a query and saw 5M files is enough for basically anyone.
This reminded me of early days running AWS SQS. We didn't charge for storage as message size was limited and the expectation was any message was going to be read immediately... But sure enough some users would just leave messages there forever and we could never figure out what they were trying to do except maybe exploit it for free storage somehow.
