There isn’t one, comparing that to storing 5M individual files in consumer cloud storage platform which is also probably missing a use case.
I store way more than 5M files on consumer storage devices all the time. It truly isn't a ridiculous number, with 2TB it's not even hard to hit with a mix of text files and smaller media files.
If the storage vendor doesn't want people to use their product for the many use-cases where you end up with a bunch of small files, advertise the file count cap. Simple as that.