>Like for example do people not end up piling them despite the deposit

If they're nice enough for piling up you've sold them for re-use that's also fine.

>and eventually throw them out?

Why throw a good fork out after storing it for a while? Might as well sell it back, keep using it or.... Even if you throw it out, but at home that's better than along the road... Where still someone would be more likely to pick it up of there's deposit on it.

It works kinda well from bottles to pallets to pressurised gas cylinders, I'm sure forks could fit in.