We offer faster NVMe drives in instances. Our E4 Dense shapes ship with SAMSUNG MZWLJ7T6HALA-00AU3, which supports Sequential Reads of 7000 MB/s, and Sequential Write 3800 MB/s.
From a general perspective, I would say the _likely_ answer to why AWS doesn't have faster NVMes at the moment is likely to be lack of specific demand. That's a guess, but that's generally how things go. If there's not enough specific demand being fed in through TAMs and the like for faster disks, upgrades are likely to be more of an after-thought, or reflecting supply chain.
I know there's a tendency when you engineer things, to just work around, or work with the constraints, and grumble amongst your team, but it's incredibly invaluable if you can make sure your account manager knows what shortcomings you've had to work around.