You need to account IO load as well, more bandwidth means more requests to the disks and I assume they will use mechanical HDDs for the storage, SSDs are still too expensive to support $0.015/GB. Good mechanical drive can give you up to 200 IOPS and maybe 200MB/s, so they will have to copy the data a lot to be able to increase capacity on demand. Making it free doesn't seems to be sustainable at all.