I have a dozen services running on a myriad of ports. My reverse proxy setup allows me to map hostnames to those services and expose only 80/443 to the web, plus the fact that an entity needs to know a hostname now instead of just an exposed port. IPS signatures can help identify abstract hostname scans and the proxy can be configured to permit only designated sources. Reverse proxies also commonly get used to allow for SSL offloading to permit clear text observation of traffic between the proxy and the backing host. Plenty of other use cases for them out there too, don’t think of it as some one trick off/on access gateway tool