> One could equally assume that a call coming from an area code they've never been to, 5 states away is spam
Not equally. I have an area code from the opposite coast. If I get a call from that area code, it is 100% spam. Spammers just love outing themselves by spoofing the same area code of the person they are calling.
A call from any other area code is only 30% chance of being spam.