When they changed their license, they were no longer open source. They could have chosen open source licenses such as the AGPL, but they did not. They were a non-open source company at that point, and AWS was putting out a product build on open source. Simple as that.

Redis was not an open source company when AWS moved to Valkey.

Companies are free to license under the AGPL if they want. Or other open source licenses.

Sorry, but non-open source companies aren't getting sympathy from me because they are hating on open source projects.