ECS Cluster with Launch Type EC2 does not create ARM64 Instances

Question

I am using ECS-CLI to provision a cluster.

This is my cluster config:

ecs-cli configure --cluster production --region ap-southeast-1 --default-launch-type EC2 --config-name production-config 

This is my command:

ecs-cli up --capability-iam \
   --keypair keyname \
   --region ap-southeast-1 \
   --launch-type EC2 \
   --size 2 \
   --instance-type t2.small \
   --ecs-profile production \
   --cluster-config production-config 
   --force --verbose

I can check my cluster status. Everything works fine.

aws ecs describe-clusters --clusters production --region ap-southeast-1

{
    "clusters": [
        {
            "clusterArn": "arn:aws:ecs:ap-southeast-1:665186350589:cluster/production",
            "clusterName": "production",
            "status": "ACTIVE",
            "registeredContainerInstancesCount": 2,
            "runningTasksCount": 1,
            "pendingTasksCount": 0,
            "activeServicesCount": 1,
            "statistics": [],
            "tags": [],
            "settings": [],
            "capacityProviders": [],
            "defaultCapacityProviderStrategy": []
        }
    ],
    "failures": []
}

However, if I were to switch to an ARM64 based instance type such as t4g.small or m6g.medium, I get:

            "registeredContainerInstancesCount": 0,

I know ap-southeast-1 supports ARM64 architecture. I have scanned the documentation but cannot find a reason this is happening.

Thanks in advance.