It should be a simple task to add that command and it is widely used. It sounds more like a business decision to not add it. It is not unusual that cloud providers make it difficult to delete data for various reasons.
Either way you can see contributions to add more commands here: https://github.com/microsoft/garnet/pulls?q=is%3Apr+add+comm...
With that said, I'm slightly skeptical of/worried about Garnet but the reason is different - it received a bit too much hype soon after going public and I'm concerned it will be subject to corporate politics that often plague projects like that.