Management doesn't want to pay taxes on inventory sitting around, nor lose a bonus over "excess" expenses over a given time frame. They'd rather deal with cross-threading a lug nut on or send a rounded drain plug back out the door than do right by the customer.
Funny enough, whenever management "Sends it out", the cars always seem to find their way back for the next service. Then it's the techs fault, since "we did it last". Now I just walk away from the car if they want to play games. No drain plug when I say "needs a drain plug"? Roll my cart away, someone else can do it. They want to con the tech into trying to reuse it, then when the pan is damaged or the plug needs extracted next time "it's your fault you did it last" so you don't get paid anything for it. I'm too smart for that nonsense.
It's easy enough to just "socialize" something like a drain plug when bought in bulk, and you really only need 4 sizes for the vast majority of cars on the road. That sort of thing, a dab of RTV, misc bolts/washers, etc is literally what shop supplies are supposedly for. The industry needs to drop that **** because the customers see right through it now as just a profit add-on that makes us look bad. Lug nuts you'd need to sell, but I can't get a set for less than ~$40 my cost for 20. We could get them for less in bulk, and that supplier doesn't always have what we need. Otherwise we're getting gouged buying singles for $4-$9/each, which obviously you can't make any margin on.