Or they're selling their product to a market where the purchaser doesn't understand how much they would need to pay if they were paying by the gigabyte (or even how to check how much they would need). Telling those people they don't need to worry about that "detail" is a key selling point. Backblaze has a product for people who understand the limitations of their consumer product and don't find them acceptable: B2, which is priced by the gigabyte.