The original private endpoints implementation required meaningful work from the service teams (ec2 networking, s3, & ddb). It also changed how the "front end" API servers handled requests and how their infrastructure was deployed (at the time?). The newer LB/ENI style privatelink abstracts away _most_ of that "per service" implementation effort at the cost of more per-request/connection work fromthe virtual network. Hence why theres more support from other services, and it includes a cost.