Why don't we eliminate the initial step of an app reserving a buffer, keep each packet in its own buffer, and once the socket it belongs to is identified hand a

Why don't we eliminate the initial step of an app reserving a buffer, keep each packet in its own buffer, and once the socket it belongs to is identified hand a pointer and ownership of that buffer back to the app? If buffers can be of fixed (max) size, you could still allow the NIC to fill a bunch of them in one go.