They don’t have to keep trucks in the same state, but they have to keep enough trucks at any given location. 135 thousand more people left California for other states in the last year than came here from other states. If U-Haul lets people take trucks anywhere they want, there’s a risk that California would run out of trucks.

The way out is to keep raising one-way fees till a) they push enough customers to full-service moving companies to achieve inbound-outbound parity, or b) it becomes financially justified to hire drivers to drive empty trucks back to CA from TX.