In fact Tor is not even considered to be an onion router by its developers, so the name The Onion Router makes no sense. They consider it to be leek routing, although the people from the Navy who originally came up with the concept of onion routing still consider Tor to be a type of onion router (I wonder if they would consider I2Ps garlic routing to be onion routing also). It probably has somewhat to do with patent trolling and Tor trying to avoid that.