Why didn the Texans retreat?
Due to their inferiority in cavalry, it would have been suicidal to venture into the open once the Mexican Army had arrived. Mexican cavalry would have caught up with them and pinned them down until the infantry arrived. And then they’d be surrounded again by overwhelming numbers, without the walls, artillery and store rooms of the fort. Also, they presumably thought they were accomplishing something by holding out where they were. If that involved danger, so be it. But Travis was not self-destructive. If he received enough reinforcements and supplies, as he requested, there was hope for successful, sustained resistance. The logistical situation meant that the Mexican army would eventually (after eating up the resources of San Antonio de Bexar) have to advance or retreat. Presumably, he assumed that successful resistance at the Alamo would eventually trigger a Mexican retreat.
