why not just pilot?
Because the loss of redundancy would be much greater than when F/E, navigator and radio operator were lost. FWIW some airlines allow one of the pilots to take a nap during cruise, but usually there has to be a CC on the deck to ensure that the other pilot doesn't nod off too.
Provided that the rumor about A350 is true, Airbus has no chance of making it unless some certifying authority makes a colossal mistake.