If you did then you would understand that there's not enough for all the Carbons and Oxygen molecules to pair up. That means there's excess Carbon to find its way onto the plug.
Lambda is different for different fuels.
So you still think an O2 sensor tells you the AFR in different parts of the cylinder? Maybe if you hung out at Innovates Forum or spent enough time there Bruce clearly explained how AFR isn't AFR because it reads the combustion after the fact. Nor does it tell you what the HC ppm is and the Carbon gas balance.