Because a lot of the organizations that take donated items are charities, and disposing of your garbage costs them money that they then cannot use to do good.
https://www.npr.org/2021/05/06/993821945/goodwill-doesnt-wan...
It's the same thing with recycling. If you "hopefully" put unrecyclable stuff in with it, all you're doing is making recycling less economically viable and increasing the chance that the batch is ruined. The sorters only have the capacity to imperfectly remove the most obviously unrecyclable trash (https://www.youtube.com/watch?v=83sYHe3jdGA), not to ponder if your yogurt container is made of the right kind of plastic or determining if every wrapper is food-stained or not. The contents of your entire recycling bin flies past their eyes in a literal second or two.
For recycling, it sounds more and more like our current systems just aren't well designed. If there is so much incidental complexity downstream that can actually ruin the recycleability of other items, we as consumers should aggressively under-recycle. But then that makes recycling that much less impactful as well. I don't know what the right answer is here other than we need to improve the sorting/processing to avoid consumers needing to understand the intricacies.
So they're paying some dude to pre-screen instead of paying a larger trash bill. It's still a cost to them. If people were a little more conscientious, those costs could be eliminated.
> But then that makes recycling that much less impactful as well. I don't know what the right answer is here other than we need to improve the sorting/processing to avoid consumers needing to understand the intricacies.
Those intricacies are not hard to learn, and the improvements you seek are probably a lot harder than you or I realize.
FWIW I think the reason why it's not that way already for recycling is to encourage people to recycle when they can. But it's clear that, at this point, the processing issue is more important than that. Then those who recycle because they want to feel good about it, can pay for the privilege. And same for donations.
Basically, if you think you are being a good steward of the earth by throwing your trash into the recycling bin, you are wrong, you are making the problem worse.
https://www.reuters.com/investigates/special-report/environm...
I am more careful with recycling, but only because I have slightly more knowledge about what to recycle since there is a somewhat helpful graphic on our city's recycling bin.
If the alternative is that I throw it in the garbage, what is the net loss by letting the workers who do this all day long decide what should be thrown in the garbage? As the OP says, they have various uses for items, so it makes sense to let them handle the sorting through of junk to decide what is ultimately landfill material. Sure, I could educate myself better about the details on what happens once I hand it over, so that time isn't being wasted, but I am, of course, lazy.