Big surprise. Contrary to the popular belief, AWS wasn't/isn't built to support Amazon.com. Some fundamental pieces are designed for Amazon.com scale, but most other services are not (ACM in this case)
Of course it's true that they don't use all AWS services, either because they don't need them or because they had something built in house earlier which works for them.
Of course it's true that they don't use all AWS services, either because they don't need them or because they had something built in house earlier which works for them.