CRDs and their controllers are perhaps the reason Kubernetes is as ubiquitous as it is today - the ability to extend clusters effortlessly is amazing and opens up the door for so many powerful capabilities.
> I don't want to write a Kubernetes controller. I don't even know why it should exist.
You can take a look at Crossplane for a good example of the capabilities that controllers allow for. They're usually encapsulated in Kubernetes add-ons and plugins, so much as you might never have to write an operating system driver yourself, you might never have to write a Kubernetes controller yourself.
One of the first really pleasant surprises I got while learning was that the kubectl command itself was extended (along with tab completion) by CRDs. So install external secrets operator and you get tab complete on those resources and actions.
> I don't want to write a Kubernetes controller. I don't even know why it should exist.
You can take a look at Crossplane for a good example of the capabilities that controllers allow for. They're usually encapsulated in Kubernetes add-ons and plugins, so much as you might never have to write an operating system driver yourself, you might never have to write a Kubernetes controller yourself.