Sure, AWS may be constantly innovating on doing things more cheaply and scalably. Sometimes, those savings get passed off to the customer; but not most of it, and not necessarily all that frequently.
Amazon competes with other cloud providers and with build-your-own continually, and use price segmentation to stay on the right side of the equation for as many people as possible, while still skimming as much premium for themselves from each user group. Historically, that’s meant big price drops in most categories that would make most one off investments obsolete - while still keeping a ton for themselves.
It also helps that S3 is an anchor product that helps them sell higher margin stuff.
Did you miss where AWS reduces prices multiple times a year? I don't know the latest figure, but as of 2018, they reduced prices 67 times since launch in 2006.
The only S3 price reduction I can find was in 2012 https://aws.amazon.com/blogs/aws/amazon-s3-price-reduction/
fwiw, a quick google search for `s3 price reduction` yields one from 2016: https://aws.amazon.com/blogs/aws/aws-storage-update-s3-glaci...
there's also one-zone s3 storage options which are cheaper as well