How much of this data is actually used?
I have a folder containing the family photos. Several gigabytes. No-one is ever, ever going to look at this. The family have no reason to look back at what we were up to on the holiday in Skegness of 1998. Yet the data still remains because.... well, it's policy to retain the family photos indefinitely.
I imagine much the same goes on at the corporate level. Gigantic mountains of useless data kept either for reasons of regulatory compliance or because storage is cheap, and it just might come in handy some day in future.