The answer to this question doesn't really matter for that reason.
The vast majority of kids are in foster care because otherwise their parents would be "unreachable" for social workers, for various reasons, like refusing psych treatment for their kid that the school insists on, like autism treatment for "difficult" children, sometimes just because they can't because treatment can only happen during working hours, but the parents need to work. Meaning they are hostages to "force change". That group is huge. Next largest group are kids suspected of a crime. Keep in mind that the way our law works kids don't have any legal rights. They may be convicted of a crime but for kids there is no difference between suspected and convicted.
The thing is, with just kids in youth services that really NEED to be somewhere the current system cannot possibly survive.
If my parents had both died during my childhood we knew we'd live with our cousins Catherine and Victoria. If somehow we didn't come with a pile of money (from insurance paying out or other mechanisms that fire when two child-rearing age people suddenly die) things would have been very tight for my Uncle and his wife but we'd have family.