I see a number of lubricants recommended for use on hunting rifles. Why is powdered graphite not an acceptable alternative?

It is nasty, messy, black stuff that makes your hands look like you just got off a shift from the Kopperston #2 mines.
Otherwise, it is perfect.
There are better options; I use CLP on everything. Inside and out.

People can tell if you pick your nose.

Graphite doesn't adhere well or stick around long enough. Needs more frequent application.
I use CLP too. Good stuff, versatile in uses. Persists quite well and good rust preventative on firearms steels in storage. Pretty sure Graphite doesn't prevent rust.

Back in 1980 I brought a reloaders estate out in all the stuff was a 4oz can of graphite.

Over the years I have played with it off an on. As barrel lube bullet lube and other lube.

I still have most of it.

It works but it is so messy I hardly ever use it.