Lights can be re-used easily, but a bike computer... they would need to setup their own rigging for the wires and the magnets, that alone would cost them money and time, and who's going to buy from them? That person well inevitably buy cheap, because of the illegitimacy, so maybe $10 or $20.
It plain doesn't seem worth it, so I must be missing something, or these things are being stolen for the joy of stealing.
Is there any value in stolen bike computers? If so how?