Why host merging is not supported in sidecars

https://istio.io/docs/ops/traffic-management/deploy-guidelines/#multiple-virtual-services-and-destination-rules-for-the-same-host

「A VirtualService can only be fragmented this way if it is bound to a gateway. Host merging is not supported in sidecars.」

Im wonder why the merging is not supported in sidecars? it’s nice feature.

I tried, for sidecars, multiple VirtualService for one host, seems only the first VirtualService is used.