I provide you with a way to easily deploy my software into your AWS. I collect an annual license fee (call it $500) for ongoing maintenance and updates, you pay the AWS bill for your usage. The software itself only uses manages services so devops is largely "free", and provides knobs that allow you to tune your specific usage and cost (data retention, rate limiting, etc).
What the software does is somewhat immaterial, but imagine any of the classic SaaS backends for things like monitoring, webhooks, log aggregation, feature flags, etc.