It's changed over the years and depends quite a bit on the state, but generally family court prefers placing wards of the state with birth parents if they're alive and known and legally able to care for a child, and if not, then either kin or "fictive kin," which is any stable adult that already has a pre-existing relationship with the child. If a child is completely abandoned and has no known family, then whoever found them is probably the best thing going all else being equal.

But no, it is not generally that easy anywhere in America. My wife and I tried for six years and it never happened. Texas completely privatized foster care licensing years back, so standards can be pretty arbitrary. Some agencies are thinly-veiled scams requiring you to purchase books or parenting classes from the founder.