It states they are EXPECTED to. And yes that is why it was set up but there was no plan for parents who refuse to help their children especially if they have high enough incomes that they don't receive aid. The student can not apply on their own even in these cases .
then I guess these students have to make the same applications that hundreds of thousands of students whose parents DO the fafsa, are found to be ineligible to any form of government subsidized aide or loans but can't help with college (not by choice-by financial reality)-
apply for scholarships (not all require fafsa application)
apply for a job.
my local town is a 'college town'. public university. there are plenty of current high school students/recent grads working and saving towards attendance. even more current college students working while attending. it may not be the easiest way, but it is a viable way.