The reason you don't see Apache setup with a proxy out front by a distro, by default, is very simple. Most people don't need it, it would be confusing to them if they ran across it, and those of us who do need it know it's trivially simple to setup.

Apache isn't setup "by default" to do lots of the things I use it for regularly, but it's flexibility allows me to setup pretty much whatever I want, however I want, very easily.