Packets don't need to be routed. Sometimes you just want to communicate with a host on the same Layer-2 network. I said "Broadcast" (not Multicast) on purpose.

Sometimes you don't even want TCP/IP on the wire. Heck, sometimes you maybe don't even want DIX Ethernet on the wire.

Anyway, this discussion is going nowhere. Handcrafting packets is possible (it's basically what the kernel does anyway), sometimes it's useful, and if you could write a user-space program that could just open /dev/eth0 and write its own handcrafted packets to that stream would be helpful.