It's probably a lot easier for them to manage EBS than per-host storage. And also probably a lot more efficient as most of that ephemeral storage is wasted, but

It's probably a lot easier for them to manage EBS than per-host storage. And also probably a lot more efficient as most of that ephemeral storage is wasted, but EBS is elastic and you can just provision what you need. For most workloads, EBS is fine, and if you don't need lots of space, it's cheaper to get c4 instances with a small EBS volume than a slower comparable c3 instance with local storage. So the savings _is_ passed along. All that said, I expect the next generation will have at least one type with a mid-range local SSD available if only because there is real demand for it. But it's not going to be cheaper than using EBS, unless you use most of the disk.