There are usually many reason: 1. Scale - S3 is big - really really big! You don’t need to care if you store one KB or several petabytes. 2. Tiers: the defaul

There are usually many reason: 1. Scale - S3 is big - really really big! You don’t need to care if you store one KB or several petabytes. 2. Tiers: the default on S3 is several way replicated storage with 11 9s of durability with high availability. However you can select from cheaper options with the trade off you are happy with. 3. Cost: S3 has reduced prices several times, you can be reasonably sure your costs will go down over time on per unit basis.