Hitler was not "directly behind" the development. You make it sound like he was the lead designer, accountant and test driver. He said "I want you to develop a car that will seat four, reach 110 km/h and cost a maximum of 1000 Reichsmark" because he wanted to make car manufacturing a significant industrial branch. The reality is that it was pretty much an empty promise. People invested in shares of VW so they could eventually get a Käfer, but very few were actually built during the war.