Why didn't Castile continue invading Portugal after the Battle of Aljubarotta?

That was during the Hundred Years War between France and England and it is possible England would have supported Portugal by sending an army and ships if Spain had been successful in invading. The major loss by Castile demonstrated weakness to other provinces like Leon and Aragon. Medieval politics changed quickly and allies often turned into enemies if there was an advantage. "Supply lines" did not really exist as they are thought of today. Armies had to live off the land and needed to occupy a large city or area with resources. Even Napoleon, 400 years later, never defeated Portugal and he had far greater resources. A small force of English and Portuguese under Wellington defeated the combined French and Spanish armies in the 18th century. The Spanish then began to fight each other. The same would probably have happened in the 14th Century.