I think it may have something to do with predictability. These days, it seems that mere revenue is not enough. Companies want predictable revenue, and subscription-based services offer a more predictable revenue stream than one-off purchases.
I bought an Office 365 sub for my daughter when she started college. I kept it after she graduated solely because $10/mo for 1TB of cloud storage isn't a terrible deal. I use it to supplement my on-site backups and encrypt everything I put up there.