I think you meant to say with earnings that high why does it not reflect in the stock price?
Low PE means just that, the price is low relative to the earnings.
The answer lies in the current lack of demand for SIRI, as demand rises so shall the price.
A reduction in the float (retiring of shares through buybacks) would create scarcity and increased demand for the shares that remain in the float after the buyback is complete, or a change in overall sentiment that would be marked by increase buying pressure and higher than average volume where inflows outpace the outflow.
Be wise my friend and learn.