I think a lot of people are afraid of the process. Some like to lease - so they are out. Some have to arrange for loans and that might be difficult and a lot of people just don't want to invest the time it takes.
Lots of reasons why people can't or won't. It appeals to some, especially in they have the money in the bank and it's a matter of how much they want to take out. US wins - they save more. And finally not everyone wants the same car and is buying at the same time so it's difficult to try and prearrange these kind of things.