Ah yes. Instance store root volumes are what we originally launched EC2 with--EBS came along 2 years later, but as data volumes only at first, with boot from EBS I think a year after that. There's a lot less fragility, and really it's just easier for our customers to create an EBS snapshot based AMI.
Before we launched the c4 instance family the vast majority of instance launches were from EBS backed AMIs, so we decided to remove a pile of complexity, and beginning with the c4 instance family, we stopped supporting instance storage root volumes on new instance families.
Before we launched the c4 instance family the vast majority of instance launches were from EBS backed AMIs, so we decided to remove a pile of complexity, and beginning with the c4 instance family, we stopped supporting instance storage root volumes on new instance families.