As someone with TBs of SSDs and HDDs laying around I am someone who agrees with your point, but this is not a good way to compare costs.

For one, this has no redundancy and doesn't factor the cost of the machine providing the storage. But also it's an upfront cost for storing 4TB. It would be implied you wouldn't literally store 4TB on the SSD because now you're out of capacity for more data. If you only have 2GB of data in a bucket then S3 is still magnitudes cheaper, faster, and more redundant than anything you could put together yourself because the cost is spread across all the users of the service.

Reality is there are so many times that S3 makes the most sense that it makes people short-circuit and always pick S3 despite the huge hidden IOPS and bandwidth costs everyone rightfully tries to point out.