Why is this even necessary?

What this project provides

1. A flat text file of sorted IAM actions, one action per line.
2. A frequent update schedule, allowing you to follow AWS's releases even before they're announced via blog/API docs.
3. A descriptive/dynamic commit message per commit, making it easy to follow releases and/or peruse the release history.

What exists that's similar

[...] a lot ... add them ...

https://github.com/rvedotrc/aws-iam-reference - the origin of this project.

https://github.com/glassechidna/trackiam and https://aktion.io/ - "A project to collate IAM actions, AWS APIs and managed policies from various public sources."

https://awsapichanges.info can't find source, best guess is it's an implementation of https://github.com/awslabs/aws-sdk-api-changes (haven't confirmed that assumption).