Font architects would have much greater incentive to create the many large and complex font sets needed for rendering cuneiform usefully. There are two main stages in reading a cuneiform text, the descriptive and the interpretive. In the descriptive phase, one establishes what cuneiform signs, or graphemes, are actually written, i.e.the text is transcribed. This stage requires minimal or no knowledge of what the text means, i.e., it is context-free. In the interpretive phase, one attempts to make sense of the transcription.
Transcription is what needs a standard encoding.