Thank you for appreciating my contribution. :) And to answer your question, because it happens too fast. Everything powers on, the voltage drops below a critical point, the CPU forgets who it is or where it is, and the reboot begins. I'm sure nowadays they make efforts to anticipate this. But back then, the industry was busy cramming increasingly powerful hardware into devices, and no one had really given any thought to how the batteries would react after years of use. Then environmental factors could make everything worse - coldness can suck dozens of percent off even a healthy battery.