The core Ingress object is super minimal, basically just "listen on ABC host+path and forward requests to XYZ service". But Ingress controllers can do all types

The core Ingress object is super minimal, basically just "listen on ABC host+path and forward requests to XYZ service". But Ingress controllers can do all types of things, and might need more context to properly route the traffic. For example, you might want HTTP requests to be automatically upgraded to HTTPS. Or your ingress controller might need specific instructions if it's handling something like a gRPC connection. You might want one Ingress object handled by Traefik and another by nginx. These types of things have been addressed by adding annotations to the Ingress object. It's honestly a pretty elegant solution to a pretty hairy problem, but it ties your YAML to a specific cluster incarnation. Of course, if you use CRD's, you're in the same situation; but the dream of k8s is portability (for me).