Envoy (Istio Proxy) always intercepts requests regardless of the virtualservice setting - istio

Question

I have 4 cases regarding istio (virtual service) configuration, and I'm curious how each case works. I will suppose that virtual service is created in namespace mynamespace.
It's obvious that in every case, traffic incoming to myapp.example.com is sent to service named myapp. However, I'm unsure about the traffic within the kubernetes cluster. When I sent cURL request from another pod (in another namespace) using command $ curl myapp.mynamespace.svc.cluster.local:8080, all the cases below seemed to be equal as same log was left at sidecar istio-proxy (envoy) alongside the myapp container.
However, I'm not sure why the traffic gets intercepted by envoy in all cases. Then what's the point in specifying mesh gateway, or specifying FQDN in hosts? I also tried sending request from a pod with and without istio-proxy enabled, but the results were the same.
Please fix me if I'm wrong ! Thank you.
Case 1
Spec:
Gateways:
external
Hosts:
myapp.example.com
Http:
Route:
Destination:
Host: myapp
Port:
Number: 8080
Case 2
Spec:
Gateways:
external
mesh
Hosts:
myapp.example.com
Http:
Route:
Destination:
Host: myapp
Port:
Number: 8080
Case 3
Spec:
Gateways:
external
Hosts:
myapp.example.com
myapp.mynamespace.svc.cluster.local
Http:
Route:
Destination:
Host: myapp
Port:
Number: 8080
Case 4
Spec:
Gateways:
external
mesh
Hosts:
myapp.example.com
myapp.mynamespace.svc.cluster.local
Http:
Route:
Destination:
Host: myapp
Port:
Number: 8080