Most users aren’t storing anywhere close to 1TB. For every user using 1TB there are probably a hundred using 1GB or less. Case in point: I subscribe to Office 365 reluctantly but don’t use OneDrive.

yeah the gym model, in other words

I have 4 O365 accounts and I have 700GB on it myself but the other 3 accounts have nothing. I doubt the average usage is more than 100GB.

because most of ppl buy 1tb/2tb plan on Dropbox and OneDrive do not use all the space? whereas s3 is pay as you go model.

For a personal product with so few size options, most of the capacity won't be used.

Glacier is worth noting as a comparison point, $4 or $1 per TB per month with more limits.

Backblaze said a couple years ago their cost to provide a low-redundancy TB per month was a bit over $3.

Those are retail rates, big users get much better pricing. Dropbox used S3 for years until finally moving to their own datacenter to be more efficient.

And like others have said, users are charged for storage that many don't use so there's a lot of revenue padding. Same model used by the other clouds for consumer storage like Google Drive.

Mostly actual use billing vs potential use billing.