According to Elon, they only expected like a 100k reservations. So having 400k reservations was a very important information for Tesla about the initial demand

According to Elon, they only expected like a 100k reservations. So having 400k reservations was a very important information for Tesla about the initial demand and gave them a few more months to plan for higher production numbers. As they asked for the refundable 1k fee with the reservations, should make sure that people are not just reserving for fun or excessive amounts.