How so? If someone loses their paper wallet, you can open threads in Internet boards. Or send some funds there with a message, describing where and how you found it. There's absolutely no manner to verify who's the one who lost their cash on the street, unless the physical wallet with the identity is also dropped.
Fiat, as in physical notes are usually accompanied with a wallet, although that's not always the case. Obvoiusly, if you just find notes on the street without anything else, it's impossible to find the true owner of those notes. However, Bitcoin wallets I wouldn't expect to find in a normal wallet (physical wallet, that stores money, and cards), since I don't really associate it with that.
If you get robbed in the streets, what do they ask for? Phone, and wallet right? So, putting your Bitcoin wallet, especially a seed in a physical traditional wallet like that would be insecure, even if carrying this information in the first place is insecure, its more so by carrying it in items that typically are targets to be stolen.
So, someone might store their wallet in non traditional ways, like a capsule on their key ring or someting along those lines. When you lose this, you'll have no accompanying information, which effectively measures it as useful as losing cash with no additional information.
Also, yeah I know several people that don't actually know Bitcointalk.org exists, despite being invested in Bitcoin. So, there's that. As well, social media tends to be avoided by a certain demographic within the Bitcoin community, especially those that value privacy so Reddit, and Twitter start getting eliminated there.