Ask HN: Why aren't p2p borrowing/lending as popular as car sharing or rental?

Just a thought on this, in the peer-to-peer space, there are many car sharing companies or room/apartment rental companies. How come there isn't a big name when it comes to borrowing/lending? Something that would work the same way as Airbnb where people could list items they own (such as books, tools, games, sporting equipment, bikes, etc). People would rent these items and pay the lender a fee. What are some potential problems with this idea?