[brendyn]

Basically because there isn't much of a difference. IPFS is basically bittorrent that breaks compatibility to add some fancy new features in exchange for more resources usage, like RAM. bittorrent v2 also does this but more modestly as it intends for torrent clients to upgrade to support it.

[viraptor]

There is a big difference in that you can reference a single file/directory from a tree using the IPFS hash, which I don't believe it's possible in BitTorrent (v1). (it's not the same as torrent's partial download) As a side effect this does deduplication so multiple IPFS trees can share the same file improving availability (and provide cheap tree updates)