Brass left at ranges is swept up and used by somebody. Likely somebody who reloads for fun. Reloading is not cost effective unless you are shooting really expensive ammo. Must sort out the different case sizes and metals, and discard damaged cases. Then you need equipment (so space and money) and time. There are risks: if you mess up and add too much powder to a cartridge, you might blow up your gun (or yourself). The possible savings: ~15 of the 30 cents per round you spent on nice new 9mm.