Layer 7 Observability " you do not want to inject Envoy sidecars to your Prometheus and Grafana pods". Why?

Hi all,

As I was going through the observability tutorial I stumbled upon that sentence. Since I want Grafana and Prometheus to run within a secured mesh I need them to inject the envoy proxy, so reading that was/is confusing.

Could someone elaborate why this is mentioned in the tutorial? Is this by design that Prometheus should run outside the mesh?

What can I do to improve my question?