Is there a fundamental reason why B2 is (and will remain) cheaper than S3, or is it just because they need to compete with AWS and once successful the prices will be the same (or higher)?
[1] https://www.backblaze.com/blog/open-source-data-storage-serv...
Also, AWS costs a lot just in traffic. A lot of people store things on S3 and then make that publicly available.
AWS is "da cloud" for a lot of people. So they ride that wave high and mighty, charging a lot for everything they can easily measure. People will just pay it and will try to [post-]rationalize how it's cheaper than other providers, because AWS is better.