You're underselling what Terraform gets used for here. What happens when you're using Terraform to manage multiple cloud accounts or even multiple cloud providers? Should it be scanning the entire host it runs on for credentials from every possible cloud, check to see that your configuration only includes resources for AWS account #XXXX, and delete everything it finds for any other account and any other provider?
Think of the footguns you're introducing if they designed it the way you suggest. What happens when you pass the provider configuration an assume role that you typo or forget to edit correctly but it's still a valid role your user credentials actually have permission to assume? It then deletes every resource that role has the power to delete because you nothing for it defined in that particular root module. Safety is more important than purity or ergonomics or devex here. Heck, that may be the core difference between ops and dev.
Think of the footguns you're introducing if they designed it the way you suggest. What happens when you pass the provider configuration an assume role that you typo or forget to edit correctly but it's still a valid role your user credentials actually have permission to assume? It then deletes every resource that role has the power to delete because you nothing for it defined in that particular root module. Safety is more important than purity or ergonomics or devex here. Heck, that may be the core difference between ops and dev.