Each Range / situation is different. I've been to unattended 'BLM'-style ranges where you're hard pressed to find much of anything.
We have nothing like that here in Houston. Too many idiots/not enough land,,,
At least 2 public outdoor Ranges here sweep it up/store it in multiple 55 gallon drums until they have 'a load' (or the price is right, not sure)
The percentage of pickers compared to non-pickers is so small, I'm not sure us pickers event put a dent in it.
I used to bring my scrap cases back to the Range/dump it in their buckets , but the RO indicated their Buyer didn't like that as the Buyer turns around and sells it as 'once-fired'. I keep / recycle them now.
My Fave Range knows I don't pick up anything I do not shoot, (or plan to shoot) They're pretty relaxed* about my picking during the cease fires.
* RO saw me picking, told him I was 'recycling'. He said that's just less he'd have to sweep up at the end of the day.
* I found a box of brass in the trash, told the RO 'stuff like that' makes me mad. He said it makes him mad too as brass makes the trash a lot heavier,,,
Life is good!