Replacing localhost with docker-localhost prevents running the collector and kafka in the same k8s pod

In docker/collector/scripts/run, localhost (loopback) is replaced with docker-localhost (docker gateway). I'm running the collector and kafka containers in the same Kubernetes pod, so KAFKA_FQDN is set to localhost. So I have to remove the weird substitution from the run-script, but why is that there in the first place?