We already saw a prime example of people using bows and arrows vs guns. Look at how the Aztecs turned out.
Actually it wasn't musketry in the field that won that war. The Spanish had allies, siegecraft, cannons, dishonorable tactics, naval superiority...and smallpox. Read some history.
Why would wastelanders make weapons that are lower tech and not as effective as other options. A bow is pretty hard to manufacture, and even then not as effective as a firearm
Ah, but how many 10mm rounds do you think you could make out of sticks and feathers and broken glass? Cuz I could make some arrows out of that. Your shiny chunk of steel is only deadly if you have ammunition for it. The whole point of improvised weaponry is that it's expedient and simple to maintain with what you can get in the field.