Why can't the devil choose good?
Angelic persons are pure spirit and have no bodies. That means that they are not subject to the limitations of change over time, as are human persons. Their choices are definitive and irrevocable, because they cannot change. Before his fall, Lucifer did have the capacity to love God and to choose good. But once he chose to oppose God, that choice was irrevocable because of his nature as a purely spiritual being.
Scripture speaks of a sin of these angels.This "fall" consists in the free choice of these created spirits, who radically and irrevocably rejected God and his reign. We find a reflection of that rebellion in the tempter's words to our first parents: "You will be like God." The devil "has sinned from the beginning"; he is "a liar and the father of lies.” It is the irrevocable character of their choice, and not a defect in the infinite divine mercy, that makes the angels' sin unforgivable. "There is no repentance for the angels after their fall, just as there is no repentance for men after death" (the Catechism 392–393).
For more information, I recommend What Spirits Are and Aren't by Frank Sheed.