why did the attackers choose planes that were headed towards california?

The attackers chose planes headed towards California mainly because these were long-distance, coast-to-coast flights with full fuel tanks, which would maximize the destruction upon impact. They targeted domestic flights that typically had fewer passengers, less resistance, and that used aircraft types the hijackers had been trained to pilot. The flights were also non-stop, allowing the terrorists to maintain control and reach their intended targets with enough fuel for significant damage. The chosen planes' routes provided strategic targets, with two planes aimed at the World Trade Center in New York and one at the Pentagon in Virginia. The fourth plane, although headed initially to California, crashed in Pennsylvania due to passenger resistance. This use of transcontinental flights was intended for coordinated surprise attacks with maximum casualties and symbolic impact.