I almost thought this was a troll it's so crazy. Of course there is a huge difference between designing a car and designing software. Manufacturing a car requires the assembly of thousands of physically pieces in a precise three-dimensional structure. The design process needs to analyse all the forces, internal and external, the car has to cope with, the flow of various fluids, electricity, changing conditions of temperature and humidity etc etc etc
If a user suddenly wanted an extra window or a periscope or larger rims half-way through the process then it's not going to be possible. With software development changes like this to an application should be easy.