You are employed at a shipping company focused on automating the provisioning of Amazon ECS clusters via AWS CloudFormation templates. Your specific task involves utilizing these templates that accept a cluster name as a parameter and deploying ECS clusters using an Auto Scaling Group. To illustrate, you initially launched the template with the parameter value 'MainCluster', resulting in the deployment of five instances distributed across two availability zones. Subsequently, you attempted to launch the template again with a different parameter value, 'SecondCluster'. Despite specifying 'SecondCluster', the instances were still launched within 'MainCluster'.

What is the root cause of this issue?