I wonder why IPFS hasn't been built on top of Bittorrent, so it could reuse some of the existing infrastructure.
For example, everybody hosting a file in IPFS could automatically become a BT seeder for that file. And searching on Pirate Bay for a certail file path / hash could make the file accessible to people who have a BT client but do not (yet) run IPFS on their machine.
Its my impression that bitswap was chosen/made, to have an easier time making "trading strategies" with other peers.
BitTorrent would for that purpose be harder to modify, and claim backwards-compatibility, so I think they went all-in, and bitswap - with pluggable "trading strategies", ie how to decide which peer to share with and how much - how to avoid free-leach and so on. There was a mention of combining ipfs with filecoin - bitswap would make that integration easier.
For example, everybody hosting a file in IPFS could automatically become a BT seeder for that file. And searching on Pirate Bay for a certail file path / hash could make the file accessible to people who have a BT client but do not (yet) run IPFS on their machine.