It's a lot easier to isolate and de-privilege your reverse proxy that needs to do nothing more than speak http/https with the outside world and some local liste

It's a lot easier to isolate and de-privilege your reverse proxy that needs to do nothing more than speak http/https with the outside world and some local listeners. The url-specific web servers you're proxying tend to need a whole lot more, at least filesystem access to serve html content, at most program execution like CGIs and interpreters. Separating these concerns makes a lot of sense, and brings little to no overhead by modern standards.