In addition to what others have said, it is important to point out that the CDK is AWS specific. Your "infrastructure" is rarely just "AWS" even if you're not multi-cloud. Terraform and Pulumi can operate on things outside of AWS like Github, Okta, Cloudflare, Datadog, Hashicorp Vault, etc.
It is nice to have one system or even repo for managing all of that.
https://www.pulumi.com/docs/intro/vs/cloud_template_transpil...