I think the obvious answer is there's not much demand, and keeping it "low" allows trickery and funny business with the virtualization layer (think: SAN, etc) that you can't do with "raw hardware speed".
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Sounds like one more excuse for AWS to obfuscate any meaning in their billing structure and take control of the narrative.
How much are they getting away with by virtualization. (Think how banks use your money for loans and stuff)
You actually don't get to really see the internals other than IOPS which doesn't help when it's gatekept already.